Systems and methods for routing vpn traffic around network disruption

ABSTRACT

Methods for using a client agent to route client requests among a plurality of appliances using transport layer information include the steps of: establishing, by a client agent executing on a client, a first transport layer connection with a first appliance of a plurality of appliances, the first appliance providing access to one or more servers; establishing, by a client agent executing on the client, a second transport layer connection with a second appliance of a plurality of appliances, the second appliance providing access to one or more servers; intercepting, by the client agent, a packet transmitted by the client; selecting, by the client agent, one of the connections to transmit the intercepted packet based on a characteristic of at least one of: the transport layer connections, the plurality of appliances, or the servers; and transmitting the intercepted packet via the selected connection.

FIELD OF THE INVENTION

The present invention relates to networking technologies, andspecifically the use of a client agent to efficiently route traffic of aclient between multiple tunnels in a network environment.

BACKGROUND OF THE INVENTION

Enterprises are increasingly being asked to provide access toapplications to employees, partners and service provides located outsidethe perimeter of the enterprise network. One approach for improving theperformance and security of remotely-accessed applications is to installan appliance within the enterprise network that performs certainfunctions to accelerate application performance and provide secureaccess. In some networks different appliances may be used to provideaccess to different resources. In some networks, a plurality ofappliances may be used to provide access to a single resource. In allthese networks, load balancing, increased performance, reduced latency,and efficient switching upon failure may be desired properties. It isthus desirable that a client accessing the resources have means forselecting the appliance to use for access in order to achieve loadbalancing, increased performance, reduced latency, and/or efficientswitching upon failure.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of allowing a client agent toopen a plurality of connections to network appliances, and thenselectively route client requests on the connections based on factorsincluding load balancing, increased performance, reduced latency, andefficient switching upon failure.

In one aspect, the present invention relates to methods for redirecting,on a client, a communication of the client to a server to upondetermining the server is not useable to communicate to the client. Inone embodiment, the method comprises the steps of: establishing, by anclient agent on a client, a transport layer connection between theclient and an intermediary appliance, the intermediary applianceproviding access to one or more servers; receiving, by the client agentfrom the intermediary appliance, address information identifying atleast one of the one or more servers available to communicate;determining, by the client agent, the transport layer connection isunusable to communicate; establishing, by the client agent, a secondtransport layer connection between the client and one of the identifiedavailable servers to bypass the appliance.

In a second aspect, the present invention relates tocomputer-implemented systems for redirecting, on a client, acommunication of the client to a server to upon determining the serveris not useable to communicate to the client. In one embodiment, thesystem comprises: a client computing device; and a client agent whichexecutes on the client, establishes a transport layer connection betweenthe client and an intermediary appliance, the intermediary applianceproviding access to one or more servers; receives, from the intermediaryappliance, address information identifying at least one of the one ormore servers available to communicate; determines, the transport layerconnection is unusable to communicate; and establishes, a secondtransport layer connection between the client and one of the identifiedavailable servers.

In a third aspect, the present invention relates to methods for using aclient agent to route client requests among a plurality of appliancesusing transport layer information. In one embodiment, the methodcomprises the steps of: establishing, by a client agent executing on aclient, a first transport layer connection with a first appliance of aplurality of appliances, the first appliance providing access to one ormore servers; establishing, by a client agent executing on the client, asecond transport layer connection with a second appliance of a pluralityof appliances, the second appliance providing access to one or moreservers; intercepting, by the client agent, a packet transmitted by theclient; selecting, by the client agent, one of the first appliance orthe second appliance to transmit the intercepted packet based on acharacteristic of at least one of: the first transport layer connection,the second transport layer connection, the plurality of appliances, orthe one or more servers; and transmitting the intercepted packet via theselected connection.

In a fourth aspect, the present invention relates tocomputer-implemented systems for using a client agent to route clientrequests using transport-layer information. In one embodiment, thesystem comprises: a client computing device; and a client agentexecuting on the client computing device which establishes a firsttransport layer connection with a first appliance of a plurality ofappliances, the first appliance providing access to one or more servers;establishes a second transport layer connection with a second applianceof a plurality of appliances, the second appliance providing access toone or more servers; intercepts a packet transmitted by the client;selects one of the first appliance or the second appliance to transmitthe intercepted packet based on a characteristic of at least one of: thefirst transport layer connection, the second transport layer connection,the plurality of appliances, or the one or more servers; and transmitsthe intercepted packet via the selected connection.

The details of various embodiments of the invention are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent and better understood byreferring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment fora client to access a server via an appliance;

FIG. 1B is a block diagram of an embodiment of an environment fordelivering a computing environment from a server to a client via anappliance;

FIGS. 1C and 1D are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance forprocessing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of an appliance foroptimizing, accelerating, load-balancing and routing communicationsbetween a client and a server;

FIG. 3 is a block diagram of an embodiment of a client for communicatingwith a server via the appliance;

FIG. 4A is a block diagram of an embodiment of a client-sideinterception mechanism;

FIG. 4B is a block diagram of an embodiment of a client-sidemultiple-tunneling mechanism;

FIG. 5 is a block diagram of a client agent with a plurality ofconnections to a plurality of appliances;

FIG. 6 is a flow diagram of steps of an embodiment of a method for usinga client agent to route client requests among a plurality of appliancesbased on characteristics of the appliances;

FIG. 7A is a block diagram of an embodiment of a system for a client tomonitor gateway appliances or resources for accessing an application ora server, and bypass a gateway appliance; and

FIG. 7B is a flow diagram of steps of an embodiment of a method formonitoring and bypassing an appliance by a client to access a server

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION A. Network and ComputingEnvironment

Prior to discussing the specifics of embodiments of the systems andmethods of an appliance and/or client, it may be helpful to discuss thenetwork and computing environments in which such embodiments may bedeployed. Referring now to FIG. 1A, an embodiment of a networkenvironment is depicted. In brief overview, the network environmentcomprises one or more clients 102 a-102 n (also generally referred to aslocal machine(s) 102, or client(s) 102) in communication with one ormore servers 106 a-106 n (also generally referred to as server(s) 106,or remote machine(s) 106) via one or more networks 104, 104′ (generallyreferred to as network 104). In some embodiments, a client 102communicates with a server 106 via an appliance 200.

Although FIG. 1A shows a network 104 and a network 104′ between theclients 102 and the servers 106, the clients 102 and the servers 106 maybe on the same network 104. The networks 104 and 104′ can be the sametype of network or different types of networks. The network 104 and/orthe network 104′ can be a local-area network (LAN), such as a companyIntranet, a metropolitan area network (MAN), or a wide area network(WAN), such as the Internet or the World Wide Web. In one embodiment,network 104′ may be a private network and network 104 may be a publicnetwork. In some embodiments, network 104 may be a private network andnetwork 104′ a public network. In another embodiment, networks 104 and104′ may both be private networks. In some embodiments, clients 102 maybe located at a branch office of a corporate enterprise communicatingvia a WAN connection over the network 104 to the servers 106 located ata corporate data center.

The network 104 and/or 104′ be any type and/or form of network and mayinclude any of the following: a point to point network, a broadcastnetwork, a wide area network, a local area network, a telecommunicationsnetwork, a data communication network, a computer network, an ATM(Asynchronous Transfer Mode) network, a SONET (Synchronous OpticalNetwork) network, a SDH (Synchronous Digital Hierarchy) network, awireless network and a wireline network. In some embodiments, thenetwork 104 may comprise a wireless link, such as an infrared channel orsatellite band. The topology of the network 104 and/or 104′ may be abus, star, or ring network topology. The network 104 and/or 104′ andnetwork topology may be of any such network or network topology as knownto those ordinarily skilled in the art capable of supporting theoperations described herein.

As shown in FIG. 1A, the appliance 200, which also may be referred to asan interface unit 200 or gateway 200, is shown between the networks 104and 104′. In some embodiments, the appliance 200 may be located onnetwork 104. For example, a branch office of a corporate enterprise maydeploy an appliance 200 at the branch office. In other embodiments, theappliance 200 may be located on network 104′. For example, an appliance200 may be located at a corporate data center. In yet anotherembodiment, a plurality of appliances 200 may be deployed on network104. In some embodiments, a plurality of appliances 200 may be deployedon network 104′. In one embodiment, a first appliance 200 communicateswith a second appliance 200′. In other embodiments, the appliance 200could be a part of any client 102 or server 106 on the same or differentnetwork 104,104′ as the client 102. One or more appliances 200 may belocated at any point in the network or network communications pathbetween a client 102 and a server 106.

In one embodiment, the system may include multiple, logically-groupedservers 106. In these embodiments, the logical group of servers may bereferred to as a server farm 38. In some of these embodiments, theserves 106 may be geographically dispersed. In some cases, a farm 38 maybe administered as a single entity. In other embodiments, the serverfarm 38 comprises a plurality of server farms 38. In one embodiment, theserver farm executes one or more applications on behalf of one or moreclients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more ofthe servers 106 can operate according to one type of operating systemplatform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond,Wash.), while one or more of the other servers 106 can operate onaccording to another type of operating system platform (e.g., Unix orLinux). The servers 106 of each farm 38 do not need to be physicallyproximate to another server 106 in the same farm 38. Thus, the group ofservers 106 logically grouped as a farm 38 may be interconnected using awide-area network (WAN) connection or medium-area network (MAN)connection. For example, a farm 38 may include servers 106 physicallylocated in different continents or different regions of a continent,country, state, city, campus, or room. Data transmission speeds betweenservers 106 in the farm 38 can be increased if the servers 106 areconnected using a local-area network (LAN) connection or some form ofdirect connection.

Servers 106 may be referred to as a file server, application server, webserver, proxy server, or gateway server. In some embodiments, a server106 may have the capacity to function as either an application server oras a master application server. In one embodiment, a server 106 mayinclude an Active Directory. The clients 102 may also be referred to asclient nodes or endpoints. In some embodiments, a client 102 has thecapacity to function as both a client node seeking access toapplications on a server and as an application server providing accessto hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In oneembodiment, the client 102 communicates directly with one of the servers106 in a farm 38. In another embodiment, the client 102 executes aprogram neighborhood application to communicate with a server 106 in afarm 38. In still another embodiment, the server 106 provides thefunctionality of a master node. In some embodiments, the client 102communicates with the server 106 in the farm 38 through a network 104.Over the network 104, the client 102 can, for example, request executionof various applications hosted by the servers 106 a-106 n in the farm 38and receive output of the results of the application execution fordisplay. In some embodiments, only the master node provides thefunctionality required to identify and provide address informationassociated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a webserver. In another embodiment, the server 106 a receives requests fromthe client 102, forwards the requests to a second server 106 b andresponds to the request by the client 102 with a response to the requestfrom the server 106 b. In still another embodiment, the server 106acquires an enumeration of applications available to the client 102 andaddress information associated with a server 106 hosting an applicationidentified by the enumeration of applications. In yet anotherembodiment, the server 106 presents the response to the request to theclient 102 using a web interface. In one embodiment, the client 102communicates directly with the server 106 to access the identifiedapplication. In another embodiment, the client 102 receives applicationoutput data, such as display data, generated by an execution of theidentified application on the server 106.

Referring now to FIG. 1B, a network environment for delivering and/oroperating a computing environment on a client 102 is depicted. In someembodiments, a server 106 includes an application delivery system 190for delivering a computing environment or an application and/or datafile to one or more clients 102. In brief overview, a client 10 is incommunication with a server 106 via network 104, 104′ and appliance 200.For example, the client 102 may reside in a remote office of a company,e.g., a branch office, and the server 106 may reside at a corporate datacenter. The client 102 comprises a client agent 120, and a computingenvironment 15. The computing environment 15 may execute or operate anapplication that accesses, processes or uses a data file. The computingenvironment 15, application and/or data file may be delivered via theappliance 200 and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of acomputing environment 15, or any portion thereof, to a client 102. Inone embodiment, the appliance 200 accelerates the delivery of thecomputing environment 15 by the application delivery system 190. Forexample, the embodiments described herein may be used to acceleratedelivery of a streaming application and data file processable by theapplication from a central corporate data center to a remote userlocation, such as a branch office of the company. In another embodiment,the appliance 200 accelerates transport layer traffic between a client102 and a server 106. The appliance 200 may provide accelerationtechniques for accelerating any transport layer payload from a server106 to a client 102, such as: 1) transport layer connection pooling, 2)transport layer connection multiplexing, 3) transport control protocolbuffering, 4) compression and 5) caching. In some embodiments, theappliance 200 provides load balancing of servers 106 in responding torequests from clients 102. In other embodiments, the appliance 200 actsas a proxy or access server to provide access to the one or more servers106. In another embodiment, the appliance 200 provides a secure virtualprivate network connection from a first network 104 of the client 102 tothe second network 104′ of the server 106, such as an SSL VPNconnection. It yet other embodiments, the appliance 200 providesapplication firewall security, control and management of the connectionand communications between a client 102 and a server 106.

In some embodiments, the application delivery management system 190provides application delivery techniques to deliver a computingenvironment to a desktop of a user, remote or otherwise, based on aplurality of execution methods and based on any authentication andauthorization policies applied via a policy engine 195. With thesetechniques, a remote user may obtain a computing environment and accessto server stored applications and data files from any network connecteddevice 100. In one embodiment, the application delivery system 190 mayreside or execute on a server 106. In another embodiment, theapplication delivery system 190 may reside or execute on a plurality ofservers 106 a-106 n. In some embodiments, the application deliverysystem 190 may execute in a server farm 38. In one embodiment, theserver 106 executing the application delivery system 190 may also storeor provide the application and data file. In another embodiment, a firstset of one or more servers 106 may execute the application deliverysystem 190, and a different server 106 n may store or provide theapplication and data file. In some embodiments, each of the applicationdelivery system 190, the application, and data file may reside or belocated on different servers. In yet another embodiment, any portion ofthe application delivery system 190 may reside, execute or be stored onor distributed to the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 15 for executing anapplication that uses or processes a data file. The client 102 vianetworks 104, 104′ and appliance 200 may request an application and datafile from the server 106. In one embodiment, the appliance 200 mayforward a request from the client 102 to the server 106. For example,the client 102 may not have the application and data file stored oraccessible locally. In response to the request, the application deliverysystem 190 and/or server 106 may deliver the application and data fileto the client 102. For example, in one embodiment, the server 106 maytransmit the application as an application stream to operate incomputing environment 15 on client 102.

In some embodiments, the application delivery system 190 comprises anyportion of the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™ and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application delivery system 190 may deliver one ormore applications to clients 102 or users via a remote-display protocolor otherwise via remote-based or server-based computing. In anotherembodiment, the application delivery system 190 may deliver one or moreapplications to clients or users via steaming of the application.

In one embodiment, the application delivery system 190 includes a policyengine 195 for controlling and managing the access to, selection ofapplication execution methods and the delivery of applications. In someembodiments, the policy engine 195 determines the one or moreapplications a user or client 102 may access. In another embodiment, thepolicy engine 195 determines how the application should be delivered tothe user or client 102, e.g., the method of execution. In someembodiments, the application delivery system 190 provides a plurality ofdelivery techniques from which to select a method of applicationexecution, such as a server-based computing, streaming or delivering theapplication locally to the client 120 for local execution.

In one embodiment, a client 102 requests execution of an applicationprogram and the application delivery system 190 comprising a server 106selects a method of executing the application program. In someembodiments, the server 106 receives credentials from the client 102. Inanother embodiment, the server 106 receives a request for an enumerationof available applications from the client 102. In one embodiment, inresponse to the request or receipt of credentials, the applicationdelivery system 190 enumerates a plurality of application programsavailable to the client 102. The application delivery system 190receives a request to execute an enumerated application. The applicationdelivery system 190 selects one of a predetermined number of methods forexecuting the enumerated application, for example, responsive to apolicy of a policy engine. The application delivery system 190 mayselect a method of execution of the application enabling the client 102to receive application-output data generated by execution of theapplication program on a server 106. The application delivery system 190may select a method of execution of the application enabling the localmachine 10 to execute the application program locally after retrieving aplurality of application files comprising the application. In yetanother embodiment, the application delivery system 190 may select amethod of execution of the application to stream the application via thenetwork 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application,which can be any type and/or form of software, program, or executableinstructions such as any type and/or form of web browser, web-basedclient, client-server application, a thin-client computing client, anActiveX control, or a Java applet, or any other type and/or form ofexecutable instructions capable of executing on client 102. In someembodiments, the application may be a server-based or a remote-basedapplication executed on behalf of the client 102 on a server 106. In oneembodiments the server 106 may display output to the client 102 usingany thin-client or remote-display protocol, such as the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash. Theapplication can use any type of protocol and it can be, for example, anHTTP client, an FTP client, an Oscar client, or a Telnet client. Inother embodiments, the application comprises any type of softwarerelated to VoIP communications, such as a soft IP telephone. In furtherembodiments, the application comprises any application related toreal-time data communications, such as applications for streaming videoand/or audio.

In some embodiments, the server 106 or a server farm 38 may be runningone or more applications, such as an application providing a thin-clientcomputing or remote display presentation application. In one embodiment,the server 106 or server farm 38 executes as an application, any portionof the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™, and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application is an ICA client, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla. In other embodiments, theapplication includes a Remote Desktop (RDP) client, developed byMicrosoft Corporation of Redmond, Wash. Also, the server 106 may run anapplication, which for example, may be an application server providingemail services such as Microsoft Exchange manufactured by the MicrosoftCorporation of Redmond, Wash., a web or Internet server, or a desktopsharing server, or a collaboration server. In some embodiments, any ofthe applications may comprise any type of hosted service or products,such as GoToMeeting™ provided by Citrix Online Division, Inc. of SantaBarbara, Calif., WebEx™ provided by WebEx, Inc. of Santa Clara, Calif.,or Microsoft Office Live Meeting provided by Microsoft Corporation ofRedmond, Wash.

The client 102, server 106, and appliance 200 may be deployed as and/orexecuted on any type and form of computing device, such as a computer,network device or appliance capable of communicating on any type andform of network and performing the operations described herein. FIGS. 1Cand 1D depict block diagrams of a computing device 100 useful forpracticing an embodiment of the client 102, server 106 or appliance 200.As shown in FIGS. 1C and 1D, each computing device 100 includes acentral processing unit 101, and a main memory unit 122. As shown inFIG. 1C, a computing device 100 may include a visual display device 124,a keyboard 126 and/or a pointing device 127, such as a mouse. Eachcomputing device 100 may also include additional optional elements, suchas one or more input/output devices 130 a-130 b (generally referred tousing reference numeral 130), and a cache memory 140 in communicationwith the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds toand processes instructions fetched from the main memory unit 122. Inmany embodiments, the central processing unit is provided by amicroprocessor unit, such as: those manufactured by Intel Corporation ofMountain View, Calif.; those manufactured by Motorola Corporation ofSchaumburg, Ill.; those manufactured by Transmeta Corporation of SantaClara, Calif.; the RS/6000 processor, those manufactured byInternational Business Machines of White Plains, N.Y.; or thosemanufactured by Advanced Micro Devices of Sunnyvale, Calif. Thecomputing device 100 may be based on any of these processors, or anyother processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storingdata and allowing any storage location to be directly accessed by themicroprocessor 101, such as Static random access memory (SRAM), BurstSRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM),Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended DataOutput RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), BurstExtended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM),synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data RateSDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM),Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The mainmemory 122 may be based on any of the above described memory chips, orany other available memory chips capable of operating as describedherein. In the embodiment shown in FIG. 1C, the processor 101communicates with main memory 122 via a system bus 150 (described inmore detail below). FIG. 1C depicts an embodiment of a computing device100 in which the processor communicates directly with main memory 122via a memory port 103. For example, in FIG. 1D the main memory 122 maybe DRDRAM.

FIG. 1D depicts an embodiment in which the main processor 101communicates directly with cache memory 140 via a secondary bus,sometimes referred to as a backside bus. In other embodiments, the mainprocessor 101 communicates with cache memory 140 using the system bus150. Cache memory 140 typically has a faster response time than mainmemory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In theembodiment shown in FIG. 1C, the processor 101 communicates with variousI/O devices 130 via a local system bus 150. Various busses may be usedto connect the central processing unit 101 to any of the I/O devices130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannelArchitecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or aNuBus. For embodiments in which the I/O device is a video display 124,the processor 101 may use an Advanced Graphics Port (AGP) to communicatewith the display 124. FIG. 1D depicts an embodiment of a computer 100 inwhich the main processor 101 communicates directly with I/O device 130via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1D also depicts anembodiment in which local busses and direct communication are mixed: theprocessor 101 communicates with I/O device 130 using a localinterconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device116, such as a floppy disk drive for receiving floppy disks such as3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive,a DVD-ROM drive, tape drives of various formats, USB device, hard-driveor any other device suitable for installing software and programs suchas any client agent 120, or portion thereof. The computing device 100may further comprise a storage device 128, such as one or more hard diskdrives or redundant arrays of independent disks, for storing anoperating system and other related software, and for storing applicationsoftware programs such as any program related to the client agent 120.Optionally, any of the installation devices 116 could also be used asthe storage device 128. Additionally, the operating system and thesoftware can be run from a bootable medium, for example, a bootable CD,such as KNOPPIX®, a bootable CD for GNU/Linux that is available as aGNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface118 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56 kb, X.25), broadband connections (e.g., ISDN, Frame Relay,ATM), wireless connections, or some combination of any or all of theabove. The network interface 118 may comprise a built-in networkadapter, network interface card, PCMCIA network card, card bus networkadapter, wireless network adapter, USB network adapter, modem or anyother device suitable for interfacing the computing device 100 to anytype of network capable of communication and performing the operationsdescribed herein.

A wide variety of I/O devices 130 a-130 n may be present in thecomputing device 100. Input devices include keyboards, mice, trackpads,trackballs, microphones, and drawing tablets. Output devices includevideo displays, speakers, inkjet printers, laser printers, anddye-sublimation printers. The I/O devices 130 may be controlled by anI/O controller 123 as shown in FIG. 1C. The I/O controller may controlone or more I/O devices such as a keyboard 126 and a pointing device127, e.g., a mouse or optical pen. Furthermore, an I/O device may alsoprovide storage 128 and/or an installation medium 116 for the computingdevice 100. In still other embodiments, the computing device 100 mayprovide USB connections to receive handheld USB storage devices such asthe USB Flash Drive line of devices manufactured by Twintech Industry,Inc. of Los Alamitos, Calif.

In some embodiments, the computing device 100 may comprise or beconnected to multiple display devices 124 a-124 n, which each may be ofthe same or different type and/or form. As such, any of the I/O devices130 a-130 n and/or the I/O controller 123 may comprise any type and/orform of suitable hardware, software, or combination of hardware andsoftware to support, enable or provide for the connection and use ofmultiple display devices 124 a-124 n by the computing device 100. Forexample, the computing device 100 may include any type and/or form ofvideo adapter, video card, driver, and/or library to interface,communicate, connect or otherwise use the display devices 124 a-124 n.In one embodiment, a video adapter may comprise multiple connectors tointerface to multiple display devices 124 a-124 n. In other embodiments,the computing device 100 may include multiple video adapters, with eachvideo adapter connected to one or more of the display devices 124 a-124n. In some embodiments, any portion of the operating system of thecomputing device 100 may be configured for using multiple displays 124a-124 n. In other embodiments, one or more of the display devices 124a-124 n may be provided by one or more other computing devices, such ascomputing devices 100 a and 100 b connected to the computing device 100,for example, via a network. These embodiments may include any type ofsoftware designed and constructed to use another computer's displaydevice as a second display device 124 a for the computing device 100.One ordinarily skilled in the art will recognize and appreciate thevarious ways and embodiments that a computing device 100 may beconfigured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 betweenthe system bus 150 and an external communication bus, such as a USB bus,an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, aFireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, aGigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, aSuper HIPPI bus, a SerialPlus bus, a SCI/LAMP bus, a FibreChannel bus,or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1C and 1D typicallyoperate under the control of operating systems, which control schedulingof tasks and access to system resources. The computing device 100 can berunning any operating system such as any of the versions of theMicrosoft® Windows operating systems, the different releases of the Unixand Linux operating systems, any version of the Mac OS® for Macintoshcomputers, any embedded operating system, any real-time operatingsystem, any open source operating system, any proprietary operatingsystem, any operating systems for mobile computing devices, or any otheroperating system capable of running on the computing device andperforming the operations described herein. Typical operating systemsinclude: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which aremanufactured by Microsoft Corporation of Redmond, Wash.; MacOS,manufactured by Apple Computer of Cupertino, California; OS/2,manufactured by International Business Machines of Armonk, N.Y.; andLinux, a freely-available operating system distributed by Caldera Corp.of Salt Lake City, Utah, or any type and/or form of a Unix operatingsystem, among others.

In other embodiments, the computing device 100 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment the computer 100 is a Treo 180,270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In thisembodiment, the Treo smart phone is operated under the control of thePalmOS operating system and includes a stylus input device as well as afive-way navigator device. Moreover, the computing device 100 can be anyworkstation, desktop computer, laptop or notebook computer, server,handheld computer, mobile telephone, any other computer, or other formof computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

B. Appliance Architecture

FIG. 2A illustrates an example embodiment of the appliance 200. Thearchitecture of the appliance 200 in FIG. 2A is provided by way ofillustration only and is not intended to be limiting. As shown in FIG.2, appliance 200 comprises a hardware layer 206 and a software layerdivided into a user space 202 and a kernel space 204.

Hardware layer 206 provides the hardware elements upon which programsand services within kernel space 204 and user space 202 are executed.Hardware layer 206 also provides the structures and elements which allowprograms and services within kernel space 204 and user space 202 tocommunicate data both internally and externally with respect toappliance 200. As shown in FIG. 2, the hardware layer 206 includes aprocessing unit 262 for executing software programs and services, amemory 264 for storing software and data, network ports 266 fortransmitting and receiving data over a network, and an encryptionprocessor 260 for performing functions related to Secure Sockets Layerprocessing of data transmitted and received over the network. In someembodiments, the central processing unit 262 may perform the functionsof the encryption processor 260 in a single processor. Additionally, thehardware layer 206 may comprise multiple processors for each of theprocessing unit 262 and the encryption processor 260. The processor 262may include any of the processors 101 described above in connection withFIGS. 1C and 1D. In some embodiments, the central processing unit 262may perform the functions of the encryption processor 260 in a singleprocessor. Additionally, the hardware layer 206 may comprise multipleprocessors for each of the processing unit 262 and the encryptionprocessor 260. For example, in one embodiment, the appliance 200comprises a first processor 262 and a second processor 262′. In otherembodiments, the processor 262 or 262′ comprises a multi-core processor.

Although the hardware layer 206 of appliance 200 is generallyillustrated with an encryption processor 260, processor 260 may be aprocessor for performing functions related to any encryption protocol,such as the Secure Socket Layer (SSL) or Transport Layer Security (TLS)protocol. In some embodiments, the processor 260 may be a generalpurpose processor (GPP), and in further embodiments, may be haveexecutable instructions for performing processing of any securityrelated protocol.

Although the hardware layer 206 of appliance 200 is illustrated withcertain elements in FIG. 2, the hardware portions or components ofappliance 200 may comprise any type and form of elements, hardware orsoftware, of a computing device, such as the computing device 100illustrated and discussed herein in conjunction with FIGS. 1C and 1D. Insome embodiments, the appliance 200 may comprise a server, gateway,router, switch, bridge or other type of computing or network device, andhave any hardware and/or software elements associated therewith.

The operating system of appliance 200 allocates, manages, or otherwisesegregates the available system memory into kernel space 204 and userspace 204. In example software architecture 200, the operating systemmay be any type and/or form of Unix operating system although theinvention is not so limited. As such, the appliance 200 can be runningany operating system such as any of the versions of the Microsoft™Windows operating systems, the different releases of the Unix and Linuxoperating systems, any version of the Mac OS® for Macintosh computers,any embedded operating system, any network operating system, anyreal-time operating system, any open source operating system, anyproprietary operating system, any operating systems for mobile computingdevices or network devices, or any other operating system capable ofrunning on the appliance 200 and performing the operations describedherein.

The kernel space 204 is reserved for running the kernel 230, includingany device drivers, kernel extensions or other kernel related software.As known to those skilled in the art, the kernel 230 is the core of theoperating system, and provides access, control, and management ofresources and hardware-related elements of the application 104. Inaccordance with an embodiment of the appliance 200, the kernel space 204also includes a number of network services or processes working inconjunction with a cache manager 232 sometimes also referred to as theintegrated cache, the benefits of which are described in detail furtherherein. Additionally, the embodiment of the kernel 230 will depend onthe embodiment of the operating system installed, configured, orotherwise used by the device 200.

In one embodiment, the device 200 comprises one network stack 267, suchas a TCP/IP based stack, for communicating with the client 102 and/orthe server 106. In one embodiment, the network stack 267 is used tocommunicate with a first network, such as network 108, and a secondnetwork 110. In some embodiments, the device 200 terminates a firsttransport layer connection, such as a TCP connection of a client 102,and establishes a second transport layer connection to a server 106 foruse by the client 102, e.g., the second transport layer connection isterminated at the appliance 200 and the server 106. The first and secondtransport layer connections may be established via a single networkstack 267. In other embodiments, the device 200 may comprise multiplenetwork stacks, for example 267 and 267′, and the first transport layerconnection may be established or terminated at one network stack 267,and the second transport layer connection on the second network stack267′. For example, one network stack may be for receiving andtransmitting network packet on a first network, and another networkstack for receiving and transmitting network packets on a secondnetwork. In one embodiment, the network stack 267 comprises a buffer 243for queuing one or more network packets for transmission by theappliance 200.

As shown in FIG. 2, the kernel space 204 includes the cache manager 232,a high-speed layer 2-7 integrated packet engine 240, an encryptionengine 234, a policy engine 236 and multi-protocol compression logic238. Running these components or processes 232, 240, 234, 236 and 238 inkernel space 204 or kernel mode instead of the user space 202 improvesthe performance of each of these components, alone and in combination.Kernel operation means that these components or processes 232, 240, 234,236 and 238 run in the core address space of the operating system of thedevice 200. For example, running the encryption engine 234 in kernelmode improves encryption performance by moving encryption and decryptionoperations to the kernel, thereby reducing the number of transitionsbetween the memory space or a kernel thread in kernel mode and thememory space or a thread in user mode. For example, data obtained inkernel mode may not need to be passed or copied to a process or threadrunning in user mode, such as from a kernel level data structure to auser level data structure. In another aspect, the number of contextswitches between kernel mode and user mode are also reduced.Additionally, synchronization of and communications between any of thecomponents or processes 232, 240, 235, 236 and 238 can be performed moreefficiently in the kernel space 204.

In some embodiments, any portion of the components 232, 240, 234, 236and 238 may run or operate in the kernel space 204, while other portionsof these components 232, 240, 234, 236 and 238 may run or operate inuser space 202. In one embodiment, the appliance 200 uses a kernel-leveldata structure providing access to any portion of one or more networkpackets, for example, a network packet comprising a request from aclient 102 or a response from a server 106. In some embodiments, thekernel-level data structure may be obtained by the packet engine 240 viaa transport layer driver interface or filter to the network stack 267.The kernel-level data structure may comprise any interface and/or dataaccessible via the kernel space 204 related to the network stack 267,network traffic or packets received or transmitted by the network stack267. In other embodiments, the kernel-level data structure may be usedby any of the components or processes 232, 240, 234, 236 and 238 toperform the desired operation of the component or process. In oneembodiment, a component 232, 240, 234, 236 and 238 is running in kernelmode 204 when using the kernel-level data structure, while in anotherembodiment, the component 232, 240, 234, 236 and 238 is running in usermode when using the kernel-level data structure. In some embodiments,the kernel-level data structure may be copied or passed to a secondkernel-level data structure, or any desired user-level data structure.

The cache manager 232 may comprise software, hardware or any combinationof software and hardware to provide cache access, control and managementof any type and form of content, such as objects or dynamicallygenerated objects served by the originating servers 106. The data,objects or content processed and stored by the cache manager 232 maycomprise data in any format, such as a markup language, or communicatedvia any protocol. In some embodiments, the cache manager 232 duplicatesoriginal data stored elsewhere or data previously computed, generated ortransmitted, in which the original data may require longer access timeto fetch, compute or otherwise obtain relative to reading a cache memoryelement. Once the data is stored in the cache memory element, future usecan be made by accessing the cached copy rather than refetching orrecomputing the original data, thereby reducing the access time. In someembodiments, the cache memory element nat comprise a data object inmemory 264 of device 200. In other embodiments, the cache memory elementmay comprise memory having a faster access time than memory 264. Inanother embodiment, the cache memory element may comrpise any type andform of storage element of the device 200, such as a portion of a harddisk. In some embodiments, the processing unit 262 may provide cachememory for use by the cache manager 232. In yet further embodiments, thecache manager 232 may use any portion and combination of memory,storage, or the processing unit for caching data, objects, and othercontent.

Furthermore, the cache manager 232 includes any logic, functions, rules,or operations to perform any embodiments of the techniques of theappliance 200 described herein. For example, the cache manager 232includes logic or functionality to invalidate objects based on theexpiration of an invalidation time period or upon receipt of aninvalidation command from a client 102 or server 106. In someembodiments, the cache manager 232 may operate as a program, service,process or task executing in the kernel space 204, and in otherembodiments, in the user space 202. In one embodiment, a first portionof the cache manager 232 executes in the user space 202 while a secondportion executes in the kernel space 204. In some embodiments, the cachemanager 232 can comprise any type of general purpose processor (GPP), orany other type of integrated circuit, such as a Field Programmable GateArray (FPGA), Programmable Logic Device (PLD), or Application SpecificIntegrated Circuit (ASIC).

The policy engine 236 may include, for example, an intelligentstatistical engine or other programmable application(s). In oneembodiment, the policy engine 236 provides a configuration mechanism toallow a user to identifying, specify, define or configure a cachingpolicy. Policy engine 236, in some embodiments, also has access tomemory to support data structures such as lookup tables or hash tablesto enable user-selected caching policy decisions. In other embodiments,the policy engine 236 may comprise any logic, rules, functions oroperations to determine and provide access, control and management ofobjects, data or content being cached by the appliance 200 in additionto access, control and management of security, network traffic, networkaccess, compression or any other function or operation performed by theappliance 200. Further examples of specific caching policies are furtherdescribed herein.

The encryption engine 234 comprises any logic, business rules, functionsor operations for handling the processing of any security relatedprotocol, such as SSL or TLS, or any function related thereto. Forexample, the encryption engine 234 encrypts and decrypts networkpackets, or any portion thereof, communicated via the appliance 200. Theencryption engine 234 may also setup or establish SSL or TLS connectionson behalf of the client 102 a-102 n, server 106 a-106 n, or appliance200. As such, the encryption engine 234 provides offloading andacceleration of SSL processing. In one embodiment, the encryption engine234 uses a tunneling protocol to provide a virtual private networkbetween a client 102 a-102 n and a server 106 a-106 n. In someembodiments, the encryption engine 234 is in communication with theEncryption processor 260. In other embodiments, the encryption engine234 comprises executable instructions running on the Encryptionprocessor 260.

The multi-protocol compression engine 238 comprises any logic, businessrules, function or operations for compressing one or more protocols of anetwork packet, such as any of the protocols used by the network stack267 of the device 200. In one embodiment, multi-protocol compressionengine 238 compresses bi-directionally between clients 102 a-102 n andservers 106 a-106 n any TCP/IP based protocol, including MessagingApplication Programming Interface (MAPI) (email), File Transfer Protocol(FTP), HyperText Transfer Protocol (HTTP), Common Internet File System(CIFS) protocol (file transfer), Independent Computing Architecture(ICA) protocol, Remote Desktop Protocol (RDP), Wireless ApplicationProtocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol.In other embodiments, multi-protocol compression engine 238 providescompression of Hypertext Markup Language (HTML) based protocols and insome embodiments, provides compression of any markup languages, such asthe Extensible Markup Language (XML). In one embodiment, themulti-protocol compression engine 238 provides compression of anyhigh-performance protocol, such as any protocol designed for appliance200 to appliance 200 communications. In another embodiment, themulti-protocol compression engine 238 compresses any payload of or anycommunication using a modified transport control protocol, such asTransaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK),TCP with large windows (TCP-LW), a congestion prediction protocol suchas the TCP-Vegas protocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 acceleratesperformance for users accessing applications via desktop clients, e.g.,Microsoft Outlook and non-Web thin clients, such as any client launchedby popular enterprise applications like Oracle, SAP and Siebel, and evenmobile clients, such as the Pocket PC. In some embodiments, themulti-protocol compression engine 238 by executing in the kernel mode204 and integrating with packet processing engine 240 accessing thenetwork stack 267 is able to compress any of the protocols carried bythe TCP/IP protocol, such as any application layer protocol.

High speed layer 2-7 integrated packet engine 240, also generallyreferred to as a packet processing engine or packet engine, isresponsible for managing the kernel-level processing of packets receivedand transmitted by appliance 200 via network ports 266. The high speedlayer 2-7 integrated packet engine 240 may comprise a buffer for queuingone or more network packets during processing, such as for receipt of anetwork packet or transmission of a network packer. Additionally, thehigh speed layer 2-7 integrated packet engine 240 is in communicationwith one or more network stacks 267 to send and receive network packetsvia network ports 266. The high speed layer 2-7 integrated packet engine240 works in conjunction with encryption engine 234, cache manager 232,policy engine 236 and multi-protocol compression logic 238. Inparticular, encryption engine 234 is configured to perform SSLprocessing of packets, policy engine 236 is configured to performfunctions related to traffic management such as request-level contentswitching and request-level cache redirection, and multi-protocolcompression logic 238 is configured to perform functions related tocompression and decompression of data.

The high speed layer 2-7 integrated packet engine 240 includes a packetprocessing timer 242. In one embodiment, the packet processing timer 242provides one or more time intervals to trigger the processing ofincoming, i.e., received, or outgoing, i.e., transmitted, networkpackets. In some embodiments, the high speed layer 2-7 integrated packetengine 240 processes network packets responsive to the timer 242. Thepacket processing timer 242 provides any type and form of signal to thepacket engine 240 to notify, trigger, or communicate a time relatedevent, interval or occurrence. In many embodiments, the packetprocessing timer 242 operates in the order of milliseconds, such as forexample 100 ms, 50 ms or 25 ms. For example, in some embodiments, thepacket processing timer 242 provides time intervals or otherwise causesa network packet to be processed by the high speed layer 2-7 integratedpacket engine 240 at a 10 ms time interval, while in other embodiments,at a 5 ms time interval, and still yet in further embodiments, as shortas a 3, 2, or 1 ms time interval. The high speed layer 2-7 integratedpacket engine 240 may be interfaced, integrated or in communication withthe encryption engine 234, cache manager 232, policy engine 236 andmulti-protocol compression engine 238 during operation. As such, any ofthe logic, functions, or operations of the encryption engine 234, cachemanager 232, policy engine 236 and multi-protocol compression logic 238may be performed responsive to the packet processing timer 242 and/orthe packet engine 240. Therefore, any of the logic, functions, oroperations of the encryption engine 234, cache manager 232, policyengine 236 and multi-protocol compression logic 238 may be performed atthe granularity of time intervals provided via the packet processingtimer 242, for example, at a time interval of less than or equal to 10ms. For example, in one embodiment, the cache manager 232 may performinvalidation of any cached objects responsive to the high speed layer2-7 integrated packet engine 240 and/or the packet processing timer 242.In another embodiment, the expiry or invalidation time of a cachedobject can be set to the same order of granularity as the time intervalof the packet processing timer 242, such as at every 10 ms

In contrast to kernel space 204, user space 202 is the memory area orportion of the operating system used by user mode applications orprograms otherwise running in user mode. A user mode application may notaccess kernel space 204 directly and uses service calls in order toaccess kernel services. As shown in FIG. 2, user space 202 of appliance200 includes a graphical user interface (GUI) 210, a command lineinterface (CLI) 212, shell services 214, health monitoring program 216,and daemon services 218. GUI 210 and CLI 212 provide a means by which asystem administrator or other user can interact with and control theoperation of appliance 200, such as via the operating system of theappliance 200 and either is user space 202 or kernel space 204. The GUI210 may be any type and form of graphical user interface and may bepresented via text, graphical or otherwise, by any type of program orapplication, such as a browser. The CLI 212 may be any type and form ofcommand line or text-based interface, such as a command line provided bythe operating system. For example, the CLI 212 may comprise a shell,which is a tool to enable users to interact with the operating system.In some embodiments, the CLI 212 may be provided via a bash, csh, tcsh,or ksh type shell. The shell services 214 comprises the programs,services, tasks, processes or executable instructions to supportinteraction with the appliance 200 or operating system by a user via theGUI 210 and/or CLI 212.

Health monitoring program 216 is used to monitor, check, report andensure that network systems are functioning properly and that users arereceiving requested content over a network. Health monitoring program216 comprises one or more programs, services, tasks, processes orexecutable instructions to provide logic, rules, functions or operationsfor monitoring any activity of the appliance 200. In some embodiments,the health monitoring program 216 intercepts and inspects any networktraffic passed via the appliance 200. In other embodiments, the healthmonitoring program 216 interfaces by any suitable means and/ormechanisms with one or more of the following: the encryption engine 234,cache manager 232, policy engine 236, multi-protocol compression logic238, packet engine 240, daemon services 218, and shell services 214. Assuch, the health monitoring program 216 may call any applicationprogramming interface (API) to determine a state, status, or health ofany portion of the appliance 200. For example, the health monitoringprogram 216 may ping or send a status inquiry on a periodic basis tocheck if a program, process, service or task is active and currentlyrunning. In another example, the health monitoring program 216 may checkany status, error or history logs provided by any program, process,service or task to determine any condition, status or error with anyportion of the appliance 200.

Daemon services 218 are programs that run continuously or in thebackground and handle periodic service requests received by appliance200. In some embodiments, a daemon service may forward the requests toother programs or processes, such as another daemon service 218 asappropriate. As known to those skilled in the art, a daemon service 218may run unattended to perform continuous or periodic system widefunctions, such as network control, or to perform any desired task. Insome embodiments, one or more daemon services 218 run in the user space202, while in other embodiments, one or more daemon services 218 run inthe kernel space.

Referring now to FIG. 2B, another embodiment of the appliance 200 isdepicted. In brief overview, the appliance 200 provides one or more ofthe following services, functionality or operations: SSL VPNconnectivity 280, switching/load balancing 284, Domain Name Serviceresolution 286, acceleration 288 and an application firewall 290 forcommunications between one or more clients 102 and one or more servers106. In one embodiment, the appliance 200 comprises any of the networkdevices manufactured by Citrix Systems, Inc. of Ft. Lauderdale Fla.,referred to as Citrix NetScaler devices. Each of the servers 106 mayprovide one or more network related services 270 a-270 n (referred to asservices 270). For example, a server 106 may provide an http service270. The appliance 200 comprises one or more virtual servers or virtualinternet protocol servers, referred to as a vServer, VIP server, or justVIP 275 a-275 n (also referred herein as vServer 275). The vServer 275receives, intercepts or otherwise processes communications between aclient 102 and a server 106 in accordance with the configuration andoperations of the appliance 200.

The vServer 275 may comprise software, hardware or any combination ofsoftware and hardware. The vServer 275 may comprise any type and form ofprogram, service, task, process or executable instructions operating inuser mode 202, kernel mode 204 or any combination thereof in theappliance 200. The vServer 275 includes any logic, functions, rules, oroperations to perform any embodiments of the techniques describedherein, such as SSL VPN 280, switching/load balancing 284, Domain NameService resolution 286, acceleration 288 and an application firewall290. In some embodiments, the vServer 275 establishes a connection to aservice 270 of a server 106. The service 275 may comprise any program,application, process, task or set of executable instructions capable ofconnecting to and communicating to the appliance 200, client 102 orvServer 275. For example, the service 275 may comprise a web server,http server, ftp, email or database server. In some embodiments, theservice 270 is a daemon process or network driver for listening,receiving and/or sending communications for an application, such asemail, database or an enterprise application. In some embodiments, theservice 270 may communicate on a specific IP address, or IP address andport.

In some embodiments, the vServer 275 applies one or more policies of thepolicy engine 236 to network communications between the client 102 andserver 106. In one embodiment, the policies are associated with aVServer 275. In another embodiment, the policies are based on a user, ora group of users. In yet another embodiment, a policy is global andapplies to one or more vServers 275 a-275 n, and any user or group ofusers communicating via the appliance 200. In some embodiments, thepolicies of the policy engine have conditions upon which the policy isapplied based on any content of the communication, such as internetprotocol address, port, protocol type, header or fields in a packet, orthe context of the communication, such as user, group of the user,vServer 275, transport layer connection, and/or identification orattributes of the client 102 or server 106.

In other embodiments, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to access the computingenvironment 15, application, and/or data file from a server 106. Inanother embodiment, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to have the application deliverysystem 190 deliver one or more of the computing environment 15,application, and/or data file. In yet another embodiment, the appliance200 establishes a VPN or SSL VPN connection based on the policy engine's236 authentication and/or authorization of a remote user or a remoteclient 103 In one embodiment, the appliance 102 controls the flow ofnetwork traffic and communication sessions based on policies of thepolicy engine 236. For example, the appliance 200 may control the accessto a computing environment 15, application or data file based on thepolicy engine 236.

In some embodiments, the vServer 275 establishes a transport layerconnection, such as a TCP or UDP connection with a client 102 via theclient agent 120. In one embodiment, the vServer 275 listens for andreceives communications from the client 102. In other embodiments, thevServer 275 establishes a transport layer connection, such as a TCP orUDP connection with a client server 106. In one embodiment, the vServer275 establishes the transport layer connection to an internet protocoladdress and port of a server 270 running on the server 106. In anotherembodiment, the vServer 275 associates a first transport layerconnection to a client 102 with a second transport layer connection tothe server 106. In some embodiments, a vServer 275 establishes a pool oftranport layer connections to a server 106 and multiplexes clientrequests via the pooled transport layer connections.

In some embodiments, the appliance 200 provides a SSL VPN connection 280between a client 102 and a server 106. For example, a client 102 on afirst network 102 requests to establish a connection to a server 106 ona second network 104′. In some embodiments, the second network 104′ isnot routable from the first network 104. In other embodiments, theclient 102 is on a public network 104 and the server 106 is on a privatenetwork 104′, such as a corporate network. In one embodiment, the clientagent 120 intercepts communications of the client 102 on the firstnetwork 104, encrypts the communications, and transmits thecommunications via a first transport layer connection to the appliance200. The appliance 200 associates the first transport layer connectionon the first network 104 to a second transport layer connection to theserver 106 on the second network 104. The appliance 200 receives theintercepted communication from the client agent 102, decrypts thecommunications, and transmits the communication to the server 106 on thesecond network 104 via the second transport layer connection. The secondtransport layer connection may be a pooled transport layer connection.As such, the appliance 200 provides an end-to-end secure transport layerconnection for the client 102 between the two networks 104, 104′.

In one embodiment, the appliance 200 hosts an intranet internet protocolor intranetIP 282 address of the client 102 on the virtual privatenetwork 104. The client 102 has a local network identifier, such as aninternet protocol (IP) address and/or host name on the first network104. When connected to the second network 104′ via the appliance 200,the appliance 200 establishes, assigns or otherwise provides anIntranetIP, which is network identifier, such as IP address and/or hostname, for the client 102 on the second network 104′. The appliance 200listens for and receives on the second or private network 104′ for anycommunications directed towards the client 102 using the client'sestablished IntranetIP 282. In one embodiment, the appliance 200 acts asor on behalf of the client 102 on the second private network 104. Forexample, in another embodiment, a vServer 275 listens for and respondsto communications to the IntranetIP 282 of the client 102. In someembodiments, if a computing device 100 on the second network 104′transmits a request, the appliance 200 processes the request as if itwere the client 102. For example, the appliance 200 may respond to aping to the client's IntranetIP 282. In another example, the appliancemay establish a connection, such as a TCP or UDP connection, withcomputing device 100 on the second network 104 requesting a connectionwith the client's IntranetIP 282.

In some embodiments, the appliance 200 provides one or more of thefollowing acceleration techniques 288 to communications between theclient 102 and server 106: 1) compression; 2) decompression; 3)Transmission Control Protocol pooling; 4) Transmission Control Protocolmultiplexing; 5) Transmission Control Protocol buffering; and 6)caching.

In one embodiment, the appliance 200 relieves servers 106 of much of theprocessing load caused by repeatedly opening and closing transportlayers connections to clients 102 by opening one or more transport layerconnections with each server 106 and maintaining these connections toallow repeated data accesses by clients via the Internet. This techniqueis referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from aclient 102 to a server 106 via a pooled transport layer connection, theappliance 200 translates or multiplexes communications by modifyingsequence number and acknowledgment numbers at the transport layerprotocol level. This is referred to as “connection multiplexing”. Insome embodiments, no application layer protocol interaction is required.For example, in the case of an in-bound packet (that is, a packetreceived from a client 102), the source network address of the packet ischanged to that of an output port of appliance 200, and the destinationnetwork address is changed to that of the intended server. In the caseof an outbound packet (that is, one received from a server 106), thesource network address is changed from that of the server 106 to that ofan output port of appliance 200 and the destination address is changedfrom that of appliance 200 to that of the requesting client 102. Thesequence numbers and acknowledgment numbers of the packet are alsotranslated to sequence numbers and acknowledgement expected by theclient 102 on the appliance's 200 transport layer connection to theclient 102. In some embodiments, the packet checksum of the transportlayer protocol is recalculated to account for these translations.

In another embodiment, the appliance 200 provides switching orload-balancing functionality 284 for communications between the client102 and server 106. In some embodiments, the appliance 200 distributestraffic and directs client requests to a server 106 based on layer 4 orapplication-layer request data. In one embodiment, although the networklayer or layer 2 of the network packet identifies a destination server106, the appliance 200 determines the server 106 to distribute thenetwork packet by application information and data carried as payload ofthe transport layer packet. In one embodiment, the health monitoringprograms 216 of the appliance 200 monitor the health of servers todetermine the server 106 for which to distribute a client's request. Insome embodiments, if the appliance 200 detects a server 106 is notavailable or has a load over a predetermined threshold, the appliance200 can direct or distribute client requests to another server 106.

In some embodiments, the appliance 200 acts as a Domain Name Service(DNS) resolver or otherwise provides resolution of a DNS request fromclients 102. In some embodiments, the appliance intercepts' a DNSrequest transmitted by the client 102. In one embodiment, the appliance200 responds to a client's DNS request with an IP address of or hostedby the appliance 200. In this embodiment, the client 102 transmitsnetwork communication for the domain name to the appliance 200. Inanother embodiment, the appliance 200 responds to a client's DNS requestwith an IP address of or hosted by a second appliance 200′. In someembodiments, the appliance 200 responds to a client's DNS request withan IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 200 provides applicationfirewall functionality 290 for communications between the client 102 andserver 106. In one embodiment, the policy engine 236 provides rules fordetecting and blocking illegitimate requests. In some embodiments, theapplication firewall 290 protects against denial of service (DoS)attacks. In other embodiments, the appliance inspects the content ofintercepted requests to identify and block application-based attacks. Insome embodiments, the rules/policy engine 236 comprises one or moreapplication firewall or security control policies for providingprotections against various classes and types of web or Internet basedvulnerabilities, such as one or more of the following: 1) bufferoverflow, 2) CGI-BIN parameter manipulation, 3) form/hidden fieldmanipulation, 4) forceful browsing, 5) cookie or session poisoning, 6)broken access control list (ACLs) or weak passwords, 7) cross-sitescripting (XSS), 8) command injection, 9) SQL injection, 10) errortriggering sensitive information leak, 11) insecure use of cryptography,12) server misconfiguration, 13) back doors and debug options, 14)website defacement, 15) platform or operating systems vulnerabilities,and 16) zero-day exploits. In an embodiment, the application firewall290 provides HTML form field protection in the form of inspecting oranalyzing the network communication for one or more of the following: 1)required fields are returned, 2) no added field allowed, 3) read-onlyand hidden field enforcement, 4) drop-down list and radio button fieldconformance, and 5) form-field max-length enforcement. In someembodiments, the application firewall 290 ensures cookies are notmodified. In other embodiments, the application firewall 290 protectsagainst forceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall 290 protectsany confidential information contained in the network communication. Theapplication firewall 290 may inspect or analyze any networkcommunication in accordance with the rules or polices of the engine 236to identify any confidential information in any field of the networkpacket. In some embodiments, the application firewall 290 identifies inthe network communication one or more occurrences of a credit cardnumber, password, social security number, name, patient code, contactinformation, and age. The encoded portion of the network communicationmay comprise these occurrences or the confidential information. Based onthese occurrences, in one embodiment, the application firewall 290 maytake a policy action on the network communication, such as preventtransmission of the network communication. In another embodiment, theapplication firewall 290 may rewrite, remove or otherwise mask suchidentified occurrence or confidential information.

C. Client Agent

Referring now to FIG. 3, an embodiment of the client agent 120 isdepicted. The client 102 includes a client agent 120 for establishingand exchanging communications with the appliance 200 and/or server 106via a network 104. In brief overview, the client 102 operates oncomputing device 100 having an operating system with a kernel mode 302and a user mode 303, and a network stack 310 with one or more layers 310a-310 b. The client 102 may have installed and/or execute one or moreapplications. In some embodiments, one or more applications maycommunicate via the network stack 310 to a network 104. One of theapplications, such as a web browser, may also include a first program322. For example, the first program 322 may be used in some embodimentsto install and/or execute the client agent 120, or any portion thereof.The client agent 120 includes an interception mechanism, or interceptor350, for intercepting network communications from the network stack 310from the one or more applications.

The network stack 310 of the client 102 may comprise any type and formof software, or hardware, or any combinations thereof, for providingconnectivity to and communications with a network. In one embodiment,the network stack 310 comprises a software implementation for a networkprotocol suite. The network stack 310 may comprise one or more networklayers, such as any networks layers of the Open Systems Interconnection(OSI) communications model as those skilled in the art recognize andappreciate. As such, the network stack 310 may comprise any type andform of protocols for any of the following layers of the OSI model: 1)physical link layer, 2) data link layer, 3) network layer, 4) transportlayer, 5) session layer, 6) presentation layer, and 7) applicationlayer. In one embodiment, the network stack 310 may comprise a transportcontrol protocol (TCP) over the network layer protocol of the internetprotocol (IP), generally referred to as TCP/IP. In some embodiments, theTCP/IP protocol may be carried over the Ethernet protocol, which maycomprise any of the family of IEEE wide-area-network (WAN) orlocal-area-network (LAN) protocols, such as those protocols covered bythe IEEE 802.3. In some embodiments, the network stack 310 comprises anytype and form of a wireless protocol, such as IEEE 802.11 and/or mobileinternet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may beused, including Messaging Application Programming Interface (MAPI)(email), File Transfer Protocol (FTP), HyperText Transfer Protocol(HTTP), Common Internet File System (CIFS) protocol (file transfer),Independent Computing Architecture (ICA) protocol, Remote DesktopProtocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol,and Voice Over IP (VoIP) protocol. In another embodiment, the networkstack 310 comprises any type and form of transport control protocol,such as a modified transport control protocol, for example a TransactionTCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP withlarge windows (TCP-LW), a congestion prediction protocol such as theTCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments,any type and form of user datagram protocol (UDP), such as UDP over IP,may be used by the network stack 310, such as for voice communicationsor real-time data communications.

Furthermore, the network stack 310 may include one or more networkdrivers supporting the one or more layers, such as a TCP driver or anetwork layer driver. The network drivers may be included as part of theoperating system of the computing device 100 or as part of any networkinterface cards or other network access components of the computingdevice 100. In some embodiments, any of the network drivers of thenetwork stack 310 may be customized, modified or adapted to provide acustom or modified portion of the network stack 310 in support of any ofthe techniques described herein. In other embodiments, the accelerationprogram 120 is designed and constructed to operate with or work inconjunction with the network stack 310 installed or otherwise providedby the operating system of the client 102.

The network stack 310 comprises any type and form of interfaces forreceiving, obtaining, providing or otherwise accessing any informationand data related to network communications of the client 102. In oneembodiment, an interface to the network stack 310 comprises anapplication programming interface (API). The interface may also compriseany function call, hooking or filtering mechanism, event or call backmechanism, or any type of interfacing technique. The network stack 310via the interface may receive or provide any type and form of datastructure, such as an object, related to functionality or operation ofthe network stack 310. For example, the data structure may compriseinformation and data related to a network packet or one or more networkpackets. In some embodiments, the data structure comprises a portion ofthe network packet processed at a protocol layer of the network stack310, such as a network packet of the transport layer. In someembodiments, the data structure 325 comprises a kernel-level datastructure, while in other embodiments, the data structure 325 comprisesa user-mode data structure. A kernel-level data structure may comprise adata structure obtained or related to a portion of the network stack 310operating in kernel-mode 302, or a network driver or other softwarerunning in kernel-mode 302, or any data structure obtained or receivedby a service, process, task, thread or other executable instructionsrunning or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 310 may execute oroperate in kernel-mode 302, for example, the data link or network layer,while other portions execute or operate in user-mode 303, such as anapplication layer of the network stack 310. For example, a first portion310 a of the network stack may provide user-mode access to the networkstack 310 to an application while a second portion 310 a of the networkstack 310 provides access to a network. In some embodiments, a firstportion 310 a of the network stack may comprise one or more upper layersof the network stack 310, such as any of layers 5-7. In otherembodiments, a second portion 310 b of the network stack 310 comprisesone or more lower layers, such as any of layers 1-4. Each of the firstportion 310 a and second portion 310 b of the network stack 310 maycomprise any portion of the network stack 310, at any one or morenetwork layers, in user-mode 203, kernel-mode, 202, or combinationsthereof, or at any portion of a network layer or interface point to anetwork layer or any portion of or interface point to the user-mode 203and kernel-mode 203.

The interceptor 350 may comprise software, hardware, or any combinationof software and hardware. In one embodiment, the interceptor 350intercept a network communication at any point in the network stack 310,and redirects or transmits the network communication to a destinationdesired, managed or controlled by the interceptor 350 or client agent120. For example, the interceptor 350 may intercept a networkcommunication of a network stack 310 of a first network and transmit thenetwork communication to the appliance 200 for transmission on a secondnetwork 104. In some embodiments, the interceptor 350 comprises any typeinterceptor 350 comprises a driver, such as a network driver constructedand designed to interface and work with the network stack 310. In someembodiments, the client agent 120 and/or interceptor 350 operates at oneor more layers of the network stack 310, such as at the transport layer.In one embodiment, the interceptor 350 comprises a filter driver,hooking mechanism, or any form and type of suitable network driverinterface that interfaces to the transport layer of the network stack,such as via the transport driver interface (TDI). In some embodiments,the interceptor 350 interfaces to a first protocol layer, such as thetransport layer and another protocol layer, such as any layer above thetransport protocol layer, for example, an application protocol layer. Inone embodiment, the interceptor 350 may comprise a driver complying withthe Network Driver Interface Specification (NDIS), or a NDIS driver. Inanother embodiment, the interceptor 350 may comprise a min-filter or amini-port driver. In one embodiment, the interceptor 350, or portionthereof, operates in kernel-mode 202. In another embodiment, theinterceptor 350, or portion thereof, operates in user-mode 203. In someembodiments, a portion of the interceptor 350 operates in kernel-mode202 while another portion of the interceptor 350 operates in user-mode203. In other embodiments, the client agent 120 operates in user-mode203 but interfaces via the interceptor 350 to a kernel-mode driver,process, service, task or portion of the operating system, such as toobtain a kernel-level data structure 225. In further embodiments, theinterceptor 350 is a user-mode application or program, such asapplication.

In one embodiment, the interceptor 350 intercepts any transport layerconnection requests. In these embodiments, the interceptor 350 executetransport layer application programming interface (API) calls to set thedestination information, such as destination IP address and/or port to adesired location for the location. In this manner, the interceptor 350intercepts and redirects the transport layer connection to a IP addressand port controlled or managed by the interceptor 350 or client agent120. In one embodiment, the interceptor 350 sets the destinationinformation for the connection to a local IP address and port of theclient 102 on which the client agent 120 is listening. For example, theclient agent 120 may comprise a proxy service listening on a local IPaddress and port for redirected transport layer communications. In someembodiments, the client agent 120 then communicates the redirectedtransport layer communication to the appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain NameService (DNS) request. In one embodiment, the client agent 120 and/orinterceptor 350 resolves the DNS request. In another embodiment, theinterceptor transmits the intercepted DNS request to the appliance 200for DNS resolution. In one embodiment, the appliance 200 resolves theDNS request and communicates the DNS response to the client agent 120.In some embodiments, the appliance 200 resolves the DNS request viaanother appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may comprise two agents120 and 120′. In one embodiment, a first agent 120 may comprise aninterceptor 350 operating at the network layer of the network stack 310.In some embodiments, the first agent 120 intercepts network layerrequests such as Internet Control Message Protocol (ICMP) requests(e.g., ping and traceroute). In other embodiments, the second agent 120′may operate at the transport layer and intercept transport layercommunications. In some embodiments, the first agent 120 interceptscommunications at one layer of the network stack 210 and interfaces withor communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interfacewith a protocol layer in a manner transparent to any other protocollayer of the network stack 310. For example, in one embodiment, theinterceptor 350 operates or interfaces with the transport layer of thenetwork stack 310 transparently to any protocol layer below thetransport layer, such as the network layer, and any protocol layer abovethe transport layer, such as the session, presentation or applicationlayer protocols. This allows the other protocol layers of the networkstack 310 to operate as desired and without modification for using theinterceptor 350. As such, the client agent 120 and/or interceptor 350can interface with the transport layer to secure, optimize, accelerate,route or load-balance any communications provided via any protocolcarried by the transport layer, such as any application layer protocolover TCP/IP.

Furthermore, the client agent 120 and/or interceptor may operate at orinterface with the network stack 310 in a manner transparent to anyapplication, a user of the client 102, and any other computing device,such as a server, in communications with the client 102. The clientagent 120 and/or interceptor 350 may be installed and/or executed on theclient 102 in a manner without modification of an application. In someembodiments, the user of the client 102 or a computing device incommunications with the client 102 are not aware of the existence,execution or operation of the client agent 120 and/or interceptor 350.As such, in some embodiments, the client agent 120 and/or interceptor350 is installed, executed, and/or operated transparently to anapplication, user of the client 102, another computing device, such as aserver, or any of the protocol layers above and/or below the protocollayer interfaced to by the interceptor 350.

The client agent 120 includes an acceleration program 302, a streamingclient 306, and/or a collection agent 304. In one embodiment, the clientagent 120 comprises an Independent Computing Architecture (ICA) client,or any portion thereof, developed by Citrix Systems, Inc. of FortLauderdale, Fla., and is also referred to as an ICA client. In someembodiments, the client 120 comprises an application streaming client306 for streaming an application from a server 106 to a client 102. Insome embodiments, the client agent 120 comprises an acceleration program302 for accelerating communications between client 102 and server 106.In another embodiment, the client agent 120 includes a collection agent304 for performing end-point detection/scanning and collecting end-pointinformation for the appliance 200 and/or server 106.

In some embodiments, the acceleration program 302 comprises aclient-side acceleration program for performing one or more accelerationtechniques to accelerate, enhance or otherwise improve a client'scommunications with and/or access to a server 106, such as accessing anapplication provided by a server 106. The logic, functions, and/oroperations of the executable instructions of the acceleration program302 may perform one or more of the following acceleration techniques: 1)multi-protocol compression, 2) transport control protocol pooling, 3)transport control protocol multiplexing, 4) transport control protocolbuffering, and 5) caching via a cache manager Additionally, theacceleration program 302 may perform encryption and/or decryption of anycommunications received and/or transmitted by the client 102. In someembodiments, the acceleration program 302 performs one or more of theacceleration techniques in an integrated manner or fashion.Additionally, the acceleration program 302 can perform compression onany of the protocols, or multiple-protocols, carried as payload ofnetwork packet of the transport layer protocol The streaming client 306comprises an application, program, process, service, task or executableinstructions for receiving and executing a streamed application from aserver 106. A server 106 may stream one or more application data filesto the streaming client 306 for playing, executing or otherwise causingto be executed the application on the client 102. In some embodiments,the server 106 transmits a set of compressed or packaged applicationdata files to the streaming client 306. In some embodiments, theplurality of application files are compressed and stored on a fileserver within an archive file such as a CAB, ZIP, SIT, TAR, JAR or otherarchives In one embodiment, the server 106 decompresses, unpackages orunarchives the application files and transmits the files to the client102. In another embodiment, the client 102 decompresses, unpackages orunarchives the application files. The streaming client 306 dynamicallyinstalls the application, or portion thereof, and executes theapplication. In one embodiment, the streaming client 306 may be anexecutable program. In some embodiments, the streaming client 306 may beable to launch another executable program.

The collection agent 304 comprises an application, program, process,service, task or executable instructions for identifying, obtainingand/or collecting information about the client 102. In some embodiments,the appliance 200 transmits the collection agent 304 to the client 102or client agent 120. The collection agent 304 may be configuredaccording to one or more policies of the policy engine 236 of theappliance. In other embodiments, the collection agent 304 transmitscollected information on the client 102 to the appliance 200. In oneembodiment, the policy engine 236 of the appliance 200 uses thecollected information to determine and provide access, authenticationand authorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 comprises an end-pointdetection and scanning mechanism, which identifies and determines one ormore attributes or characteristics of the client. For example, thecollection agent 304 may identify and determine any one or more of thefollowing client-side attributes: 1) the operating system an/or aversion of an operating system, 2) a service pack of the operatingsystem, 3) a running service, 4) a running process, and 5) a file. Thecollection agent 304 may also identify and determine the presence orversions of any one or more of the following on the client: 1) antivirussoftware, 2) personal firewall software, 3) anti-spam software, and 4)internet security software. The policy engine 236 may have one or morepolicies based on any one or more of the attributes or characteristicsof the client or client-side attributes.

In some embodiments and still referring to FIG. 3, a first program 322may be used to install and/or execute the client agent 120, or portionthereof, such as the interceptor 350, automatically, silently,transparently, or otherwise. In one embodiment, the first program 322comprises a plugin component, such an ActiveX control or Java control orscript that is loaded into and executed by an application. For example,the first program comprises an ActiveX control loaded and run by a webbrowser application, such as in the memory space or context of theapplication. In another embodiment, the first program 322 comprises aset of executable instructions loaded into and run by the application,such as a browser. In one embodiment, the first program 322 comprises adesigned and constructed program to install the client agent 120. Insome embodiments, the first program 322 obtains, downloads, or receivesthe client agent 120 via the network from another computing device. Inanother embodiment, the first program 322 is an installer program or aplug and play manager for installing programs, such as network drivers,on the operating system of the client 102.

D. Application Routing Table

Referring now to FIGS. 4A and 4B, embodiments of a system for providingan application routing table to a client for fine-grained client-sideinterception and client-side multiple tunneling is depicted. FIG. 4Adepicts an embodiment of an application routing table for client-sideinterception while FIG. 4B depicts an application routing table forclient-side multiple tunneling. The application routing table may beconfigured on the appliance 200 and transmitted to one or more clients102 accessing a network 104 or server 106 via the appliance 200.

Referring now to FIG. 4A, the appliance 200 and client agent 120provides a more granular mechanism via an application routing table 400for intercepting communications of a client 102 having a connection,such as an SSL VPN connection, to network 104′ via the appliance 200. Inbrief overview, the appliance 200 comprises an application routing table400. The application routing table (ART) 400 provides a networkdestination description 410 and/or a client application identifier 450.In some embodiments, the application routing table 400 via the networkdestination description identifies the applications or services 270 onservers 106 which are authorized for access by a client 102. In otherembodiments, the application routing table 400 identifies via the clientapplication identifier 450 an application running on the client 102 thatmay be authorized for a level of access to the server 106, or a service270 of the server 106. The appliance 200 may transmit the applicationrouting table 400 to the client 102 or client agent 120. The clientagent 120 uses the application routing table 400 to make determinationon whether to intercept and transmit client network communication to theappliance 200, such as via a SSL VPN tunnel to appliance, based on theapplication routing table 400.

The application routing table 400 comprises any type and form of table,database, object or data structure for arranging and storing informationas described herein. In some embodiments, the application routing table400 is populated, configured, created, edited or modified via a commandline interface 212 or graphical user interface 210 of the appliance. Inother embodiments, application routing table 400 is populated,configured, created, edited or modified via the client 102, server 106or another computing device 100. In one embodiment, the client 102receives the application routing table 400 from the appliance 200. Forexample, the client agent 120 receives the application routing table 400upon establishing a connection with the appliance 200. In anotherexample, the client agent 120 downloads the application routing table400 from a server, a web-site or any other computing device 100 on thenetwork 104. In another embodiment, a user creates or modifies theapplication routing table 400 on the client 102.

In some embodiments, the application routing table 400 comprises one ormore network destination descriptions 410. The network destinationdescription 410 may comprise information identifying one or more of thefollowing: a destination network identifier 415, a destination port 420,a protocol 425, a source network identifier 430, a source port 435, andan intranet application name 440. The destination network identifier 415and source network identifier 430 may comprise a host or domain name,and/or an internet protocol address. In some embodiments, destinationnetwork identifier 415 and source network identifier 430 comprises arange of internet protocol addresses, a list of internet protocoladdresses and/or a list of domain or host names. The destination port420 and source port 435 identifies one or more port numbers for anetwork communication end-point. For example, the destination port 430may identify port 80 for http traffic an http or web-server. In anotherexample, the destination port 430 may identify port 21 for file transferprotocol (ftp). In some embodiments, the protocol identifier 425identifies one or more types of protocol by name, number, version orapplication. In other embodiment, the protocol identifier 425 identifiesthe protocol by layer of the network stack, such as Layer 1-7. In oneembodiment, the intranet application name 440 identifies a name oridentifier of an application associated with the destination networkidentifier 415 and/or destination port 420. For example, the intranetapplication name 440 may identify a name of the email, database, or acorporate application being accessed via the destination networkidentifier 415 and/or destination port 420.

In one embodiment, the network destination description 410 identifies byinternet protocol layer information or network layer information alocation of an application or service 270 on a network 104. For example,a destination network identifier 415 and destination port 420 mayidentify a destination location of an application on a network 104. Insome embodiments, the network destination description 410 identifies adestination authorized for access via the appliance 200. In anotherembodiment, the network destination description 410 identifies byinternet protocol layer information or network layer information alocation of a client accessing the application or service 270 of aserver 106 via the network 104. For example, a destination networkidentifier 415 and destination port 420 may identify a destinationlocation of an application on a network. In some embodiments, thenetwork destination description 410 identifies a client authorized toaccess the network 104 or server 106 via the appliance 200. In yetanother embodiment, the network destination description identifies byinternet protocol or network layer information the source anddestination of traffic flow between a client 102 and a server 106. Inone embodiment, the network destination description 410 identifies atraffic flow between a client 102 and server 106 authorized for accessvia the appliance 200.

In some embodiments, the application routing table 400 comprises one ormore client application identifiers 450. The client applicationidentifier 450 identifies an application installed or operating on theclient 102 authorized for access to a network 104 or a server 106 viathe appliance 200. In one embodiment, the client application identifier450 comprises a name of an executable file for the application, such asthe name of the .exe file of the application. For example, the clientapplication identifier 405 may include the name “explorer.exe”,“outlook.exe” or “winword.exe”. In other embodiments, the clientapplication identifier 450 identifies an image name of a process orexecutable. In another embodiment, the client application identifier 450comprises a name of a script. In yet another embodiment, the clientapplication identifier 450 comprises a name of a process, task orservice that may or is operating on the client 102. In still anotherembodiment, the client application identifier 450 comprises a processidentifier, or PID, or a range of PIDS.

In one embodiment, the policy engine 236 of the appliance 200 comprisesone or more rules associated with the application routing table 400, orany portion thereof. In some embodiments, the policy engine 236comprises a policy for access, authorization, and/or auditing based on anetwork destination description 410. In other embodiments, the policyengine 236 comprises a policy for access, authorization, and/or auditingbased on a client application identifier 450. In another embodiment, thepolicy engine 236 comprises a policy for session and/or trafficmanagement policies based on the network destination description 410and/or client application identifier 450. In yet another embodiment, theclient 102 comprises a policy engine 236 for applying one or morepolicies or rules based on the network destination description 410and/or client application identifier 450.

In operation, the client agent 120 uses the application routing table400 for determining the network communications on the network stack 310to intercept. In one embodiment, the client agent 120 intercepts networkcommunication having information identifying or corresponding to anetwork destination description 410. For example, the client agent 120may intercept a network packet on the network stack 310 destined for adestination network identifier 415 and/or destination port 420 of anetwork destination description 410 of an application routing table 400.In another embodiment, the client agent 120 intercepts networkcommunications on the network stack 310 originating from an applicationon the client 102 corresponding to a client application identifier 450of the application routing table 400. In other embodiments, the clientagent 120 does not intercept network communications on the network stack310 that do not correspond to either a network destination description410 or a client application identifier 450.

Referring now to FIG. 4B, the appliance 200 and client agent 120provides a mechanism via the application routing table 400 forestablishing multiple client-side connections to multiple appliances orvServers 275 to access a server 106 via the appliance 200. In briefoverview of this embodiment, the application routing table 400 comprisesinformation identifying one or more resources (gateways, servers, orappliances, or vServers of appliances) for a client 102 to access anintranet application 440 on a network 104 accessed via the one or moreresources. The client agent 120 receives the application routing table400 and establishes a transport layer connection to each of theresources identified by the application routing table. The client agent120 monitors the status of each of these resources to make switching,routing and/or load balancing decisions for the client 102 to access theapplication 440.

As illustrated in FIG. 4B, an embodiment of the application routingtable 400 comprises a resource description 411 for each of the one ormore resources identified as a resource to access an identifiedapplication 440 via the appliance 200. The application routing table 400may comprise multiple sets of resource descriptions 411 for a pluralityof applications 440 access by the appliance 200. In one embodiment, anapplication routing table may comprise an enumerated list of resourcedescriptions 413 corresponding to resources which provide access to aparticular application. The enumerated list 413 may be sorted by anycriteria, including without limitation availability, performance, anddistance from a client. For example, an application routing table maycomprise a list 413 of three appliances through which a client mayaccess a given word processing program, where the three appliances areranked in order of their geographical distance from a client 102.

In one embodiment, a resource description 411 may comprise some or allof the information contained in a network destination description 410.In one embodiment, the resource description 411 includes a networkidentifier 415, a port 420, a protocol 425, and/or a status 460. Thenetwork identifier 415 comprises an internet protocol address and/orhost name of the resource. In one embodiment, the resource comprises anappliance 200. In another embodiment, the resource comprises a server106. In other embodiments, the resource comprises a gateway, networkdevice or computing device 100. In yet another embodiment, the resourcecomprises a vServer 275 of an appliance 200. The port 420 comprises anetwork port, such as a destination port identifier, of the resource. Inone embodiment, the port 420 identifies to the client agent 120 a portof the resource to connect to. In another embodiment, the port 420identifies to the client agent 120 a port of the resource to connectfrom. In one embodiment, the protocol 425 comprises a name, type oridentifier of the protocol used to access the application identified bythe intranet application name 440. In other embodiments, the protocol425 comprises a name, type or identifier of the protocol used to connector communicate with the resource. The application routing table 400 mayalso include a field or parameter for indicating status 460. In oneembodiment, the appliance 400 indicates an initial or current status ofthe resource associated with the resource description 411. In otherembodiments, the status 460 is used by the client agent 120 formonitoring and updating the status of any resource. The appliance 200and/or client agent 120 may indicate, identify or describe the status460 for a resource using any type and form of identifier, such as astring, text, numbers, characters, symbols, or any combination thereof.Status 460 may include any operational characteristic of the resource ora connection to the resource including without limitation capacity,load, and performance.

In the embodiment shown, an application routing table 400 comprising atleast one resource list 413 is transmitted to a client 102. In someembodiments, the application routing table may be transmitted to theclient upon establishment of a connection with the appliance. In otherembodiments, the application routing table 400 may be sent in responseto a request from the client. In one embodiment, portions of theapplication routing table may be transmitted at different times. Inanother embodiment, an appliance may transmit periodic updates to anapplication routing table. These updates may comprise informationadding, removing, or modifying any resource list 413 or resourcedescription 411 contained in the application routing table. As will befurther described with respect to FIGS. 5-7B, the client agent may thenuse the information in the application routing table 400, the resourcelists 413, and resource descriptions to open one or more connectionswith identified resources and to efficiently route client requests.

E. Multiple Client-Side Tunneling

Referring now to FIG. 5, a client agent with a plurality of connectionsto a plurality of appliances is shown. In brief overview, a client agent120 may open a plurality of connections to a plurality of appliances 200a, 200 b, 200 c. The client agent 120 may use a monitor 500 to receive,via the plurality of connections, status information relating to theplurality of appliances 200 a, 200 b, 200 c, and one or more servers 106a, 106 b to which the appliances provide access.

Still referring to FIG. 5, now in greater detail, a client agent 120 isconnected to a plurality of appliances 200 which provide access to anumber of servers 106. These connections may be any connection describedherein, including SSL VPN connections. Although in the embodiment shown,the connections are to a plurality of appliances, in other embodiments,the plurality of connections may comprise one or more connections to anyresource, including gateways, servers, or appliances, or vServers ofappliances. The client agent 120 may establish the plurality ofconnections in response to receiving an application routing table 400comprising a resource list 413 for a given application the client 102has requested. In one embodiment, the client agent 120 may establish aconnection to every resource on the resource list corresponding to arequested application. In another embodiment, the client agent 120 mayestablish a connection to a predetermined number of resources on theresource list. In still another embodiment, the client agent 120 mayonly establish a connection to resources on the resource list with agiven characteristic or characteristic. For example, the client agent120 may make connections with only resources having a givenavailability, or resources only a given distance from the client.

After opening the plurality of connections, the client agent may monitorthe status of the plurality of connections and the plurality ofresources using a monitor program 500. The monitor program 400 maycomprise software, hardware or any combination of software and hardware.The monitor program 400 may comprise an application, service, process,task or thread. The monitor program 500 may comprise logic, function oroperations for monitoring a status of a resource.

The monitor 500 may update the application routing table withinformation received relating to the status of the plurality ofresources. The monitor may 500 receive status information from theresources using any protocol or protocols, including without limitationping requests, and heartbeat token protocols. In some embodiments, theresources may send status information to the client agent atpredetermined intervals. In other embodiments, the resources may sendstatus information in response to a change in status. For example, aresource may send updated status information if the resource experiencesan increase in load causing the resource's availability status tochange. In some embodiments, a first resource may send statusinformation identifying a status of a second resource. For example, anappliance 200 providing access to a sever 106 may monitor the status ofthe server, and then transmit information to a client agent 120identifying the server status. Or for example, a vServer 275 running onan appliance may transmit status information to a client agent 120identifying the status of a second vServer running on the sameappliance.

Referring now to FIG. 6, one embodiment of a method for using a clientagent to route client requests among a plurality of appliances based oncharacteristics of the appliances is shown. In brief overview, themethod comprises establishing, by a client agent executing on a client,a first transport layer connection with a first appliance of a pluralityof appliances, the first appliance providing access to one or moreservers (step 601); establishing, by a client agent executing on theclient, a second transport layer connection with a second appliance of aplurality of appliances, the second appliance providing access to one ormore servers (step 603); receiving, by the client agent from one or moreof the plurality of appliances, information identifying a characteristicof at least one of: the first transport layer connection, the secondtransport layer connection, one or more of the plurality of appliances,or one or more servers (step 605); intercepting, by the client agent, apacket transmitted by the client (step 607); selecting, by the clientagent, one of the first appliance or the second appliance to transmitthe intercepted packet based on a characteristic of at least one of: thefirst transport layer connection, the second transport layer connection,the plurality of appliances, or the one or more servers (step 609); andtransmitting the intercepted packet via the selected connection (step611).

Still referring to FIG. 6, now in greater detail, a client agentexecuting on a client, establishes a first transport layer connectionwith a first appliance of a plurality of appliance. The first applianceprovides access to one or more servers (step 601). The transport layerconnection may comprise any type or form of transport layer connection,including without limitation an SSL VPN connection. The connection maycomprise the same type of connection used to access an application viathe appliance. In some embodiments, the client agent may establish aconnection with a vServer running on an appliance.

After opening a first transport layer connection to an appliance (step601), the client agent may then establish a second transport layerconnection with a second appliance of a plurality of appliances, thesecond appliance providing access to one or more servers (step 603). Insome embodiments, the second appliance may be a physical appliance. Thisconnection may be established in the same manner as the firstconnection. In some embodiments, the client agent may establish a secondconnection with a vServer running on an appliance. In one embodiment,the client agent may establish two or more connections with the sameappliance. In another embodiment, the client agent may establish aplurality of connections with a plurality of vServers running on anappliance.

In some embodiments, the establishment of the first and secondconnections may be responsive to receiving an application routing table400 comprising a resource list 413 corresponding to an application theclient desires and identifying the first and second appliances asresources providing access to the application. The client agent mayselect one or more of the appliances to connect to based on anycharacteristic of the appliances. In some embodiments, the client agentmay open a plurality of connections to appliances providing access to anapplication server.

After establishing the second transport layer connection (step 605), theclient agent may information identifying a characteristic of at leastone of: the first transport layer connection, the second transport layerconnection, one or more of the plurality of appliances, or one or moreservers (607). This information may be received by any means describedherein, including as an application routing table 400 or an update to anapplication routing table 400, or as status information received fromone of the plurality of appliances. A characteristic of the firsttransport layer connection, the second transport layer connection, oneor more of the plurality of appliances, or one or more servers maycomprise any characteristic including without limitation: availability,performance, capacity, load, usage, bandwidth, latency, geographicdistance, and past statistics.

After receiving information identifying at least one characteristic(step 607), the client agent may then intercept a packet transmitted bythe client (step 609). The packet may be intercepted using any meansdescribed herein, including the use of a TDI driver. The packet maycorrespond to an application being accessed remotely.

After intercepting the packet (step 609), the client agent may selectone of the first appliance or the second appliance to transmit theintercepted packet based on a characteristic of at least one of: thefirst transport layer connection, the second transport layer connection,the plurality of appliances, or the one or more servers (step 611). Theclient agent may first determine, using any technique described herein,that the packet corresponds to a given application. The client agent maythen determine which of the client agent's open connections toappliances is capable of servicing packets corresponding to the givenapplication. The client agent may then determine which of the openconnections capable of servicing packets for the given application tosend the packet on, based on one or more characteristics. In someembodiments, the determination may be performed by a policy engine.

The client agent may select a connection or resource in order to performany network function including without limitation load balancing,switching, failover, acceleration, and efficient caching. For example, aclient agent may intercept a packet, and determine the packetcorresponds to a remotely executing database application. The clientagent may have two connections currently open to appliances capable ofservicing packets intended for the database application server. Theclient agent may determine that a first connection is currentlyinoperational, and thus select the second connection for transmission ofthe packet.

Or for example, a client agent may intercept a packet, and determine thepacket corresponds to a remotely executing word processing application.The client agent may have three connections currently open to vServerscapable of servicing packets intended for the word processingapplication server. The client agent may select a connection byidentifying the vServer with the lowest current usage. Or the clientagent may select a connection by identifying the vServer with the lowestlatency.

Or for example, a client agent may have three connections currently opento vServers capable of servicing packets intended for the wordprocessing application server. The client agent may determine that oneof the connections has a slightly lower latency, but select theconnection used to transmit previous packets to the word processingapplication server, such that a cache residing on the appliance may beoptimally used.

After selecting a connection (step 411), the client agent may thentransmit the intercepted packet via the selected connection. Thistransmission may be done via any of the means described herein.

In one illustrative embodiment, a client agent may connect to a firstappliance which serves as a base appliance. The base appliance maytransmit an application routing table to the client agent. The clientagent may then establish connections with a route requests forapplications to a plurality of appliances based on the applicationrouting table. The plurality of appliances may or may not then includethe base appliance.

As another illustrative example, a client agent may performload-balancing functions by establishing a plurality of connections witha plurality of appliances providing access to an application. The clientagent may then determine based on load-balancing factors whichconnection to send client packets corresponding to the application. Forexample, the client agent may utilize a round-robin approach, whereineach successive packet is sent to a different appliance. Or for example,the client agent may send each packet to the appliance with the fewestnumber of currently open or active connections.

As a third illustrative example, a client agent may perform accelerationby establishing a plurality of connections with a plurality ofappliances providing access to an application. The client agent mayselect the connection based on connection speed to send client packetscorresponding to the application. For example, the client agent mayselect the connection with the lowest latency, or the highestthroughput.

F. Monitoring and ByPassing an Appliance

In view of FIGS. 7A and 7B, an embodiment of a system for monitoring andbypassing an appliance by a client to access an application or a serveris depicted. Referring now to FIG. 7A, an embodiment of a system isdepicted for a client 102 to monitor gateway appliances or resources foraccessing an application or a server 106, and bypass a gateway appliance200 or resource when it is not available in order to continue accessingthe application or server 106. In brief overview, a client 102, viaclient agent 120, received an application routing table 400 identifyingone or more resources via which the client 102 can access an applicationor a server 106. The client agent 120 may establish one or moretransport layer connections with each of the resources identified by theapplication routing table 400. The client 102 may access the applicationor server 106 via a first selected resource, such as a first appliance200A. For example, the application routing table 400 may provide anordered enumerated list of resources for accessing the application orserver 106. The client agent 120, via the monitor 500, monitors thestatus 460 of each of the resources. If the client agent 120 determinesthe first selected resource is not available or not useable to accessthe application or server 106, the client agent automatically bypassesthe unusable resource. In one case, the client 120 may establish asecond transport layer connection directly to the application or server106. In another case, the client 120 may establish the second transportlayer connection with another resource or second appliance in order toaccess the application or server 106. For example, the client agent 120may select a second appliance 200B from the ordered enumerated list ofgateway resources 410 identified by the application routing table 400,and establish the second transport layer connection with this secondappliance 200B.

As illustrated in FIG. 7A, a client 102 may access an application oneither a first server 106A or a second server 106B. That is, in someembodiments, the first server 106A and second server 106B may provideaccess to the same application or service 270. In this example, a firstappliance 200A provides access to the first server 106A, and a secondappliance 200B and third appliance 200C provide access to the secondserver 106B. Additionally, the client 102 may access either the firstserver 106A or the second server 106B directly. In some embodiments, theclient 102 may access the servers 106A-106B via an appliance 200 toaccess the services, functionality or operations of the appliance 200,such as acceleration, load-balancing, application firewall or SSL VPNfunctionality. However, if an appliance 200, or a vServer 275 of theappliance 200, is not available or is otherwise unusable, the client 102may bypass the appliance 200, and functionality thereof, to gain or tocontinue access to the application or server 106.

The client agent 120, via monitor 500, may monitor any of the appliances200A-200C and/or any of the servers 106A-106B to determine the status ofeach. Based on the status of these resources, the client agent 120 canmake routing or load-balancing decisions to bypass any appliance 200 atany time to continue or gain access to one of the servers 106A-106B. Forexample, the client 102 may establish one connection with the secondappliance 200B to access the server 106B. If the second appliance 200Bgoes down or is otherwise not operational, the client 102 via the clientagent 120 may automatically establish a transport layer connection tothe server 106B directly to bypass the appliance 200B. In anotherexample, the client 102 may establish a first transport layer connectionwith the second appliance 200B and a second transport layer connectionwith the third appliance 200C. The client 102 may first access theserver 106B via the second appliance 200B. If the client 102 detects viamonitoring that the second appliance 200B is not usable to access theserver 106B, the client 102 may automatically switch to using the secondtransport layer connection already established with the third appliance200C. If client 102 then detects via monitoring that the third appliance200C becomes unusable, then the client 102 may automatically establish athird transport layer connection to the server 106B directly.

In other embodiments, the application routing table 400 may identify viathe resource description 411 one or more vServers 275 on the sameappliance 200 or across multiple appliances 200. For example, in oneembodiment, the client 102 may establish a transport layer connectionwith one vServer 275A of appliance 200. If the client 102 detects thevServer 275A is unavailable or unusable, the client 102 mayautomatically establish a second transport layer connection with asecond vServer 275A or directly to the server 106. In some embodiments,the client 102 establishes a plurality of transport layer connectionswith a plurality of vServers 275. In some embodiments, the vServers 275are on the same appliance 200, while, in other embodiments, the vServersare on different appliances 200. As such, in one embodiment, the client102 can automatically bypass any vServer 275 to access the server 106.

Referring now to FIG. 7B, steps of an embodiment of a method 700 formonitoring and bypassing an appliance by a client to access a server isdepicted. In brief overview, at step 705, the method includesestablishing, by a client agent, a transport layer connection between aclient and one or more appliances 200. The appliances 200 provide accessto one or more applications 270 or servers 106. At step 710, the clientagent 120 receives or obtains an application routing table 400. At step715, the client agent 120 via the monitor 500 monitors the status ofresources identified by the application routing table 400, such as theone or more appliances or the one or more applications and/or servers.At step 720, the client agent 120 determines via monitoring that thestatus of the resources indicates an appliance or resource is notuseable by the client to communicate to the server. At step 725, theclient agent 120, automatically in response to the determination,establishes a second transport layer connection between the client and aresource or the server to bypass the appliance identified as unusable.

In further detail, at step 705, the client 102 establishes any type andform of connection with an appliance 200. In some embodiments, theclient agent 102 establishes a transport layer connection with theappliance 200, such as via the transport control protocol or userdatagram protocol. In one embodiment, the client agent 120 establishes atunnel connection with the appliance 200 using any type and form oftunneling protocol. In another embodiment, the client agent 120establishes a virtual private network connection via the appliance 200to a network 104. For example, the client agent 120 may establish avirtual private network connection with the appliance 200 to connect theclient 102 on the first network 104 to a second network 104′. In someembodiments, the client agent 120 establishes a SSL VPN connection withthe appliance 200. In yet another embodiment, the client agent 120establishes a tunnel or virtual private network connection usingTransport Layer Secure (TLS) protocol. In one embodiment, the clientagent 120 establishes a tunnel connection using the Common GatewayProtocol (CGP) manufactured by Citrix Systems, Inc. of Ft. Lauderdale,Fla. In yet other embodiments, the client 102 or client agent 120establishes a transport layer connection with one or more vServers 275.In some embodiments, the client 102 or client agent 120 establishes aplurality of transport layer connections with a plurality of resources,such as appliances 200, vServers 275, and servers 106.

At step 710, the client agent 120 obtains or receives an applicationrouting table 400 from the appliance 200, a user of the client 102, or acomputing device 100. In one embodiment, the client agent 120 receivesthe application routing table 400 upon establishing a connection withthe appliance 200. For example, the client agent 120 may request theapplication routing table 400 from the appliance 200. In anotherembodiment, the appliance 400 transmits the application routing table400 to the client agent 120. For example, if a change to the applicationrouting table 400 is made, the appliance 200 may transmit or push thechanges to the client agent 120. In some embodiments, the client agent120 loads or opens the application routing table 400 from storage on theclient 120 or a computing device 100 accessible via the network 104. Inyet another embodiment, the client agent 120 downloads the applicationrouting table 400 from a web-site, such as via http. In a furtherembodiment, the client agent 120 transfers a file having the applicationrouting table 400 via a file transfer protocol (FTP). In one embodiment,a user creates or generates the application routing table on the client120. In another embodiment, a user configures the client agent 120 tohave the application routing table 400.

In some embodiments, the client agent 120 establishes a transport layerconnection to a resource (e.g., appliance 200, vServer 275, or server106) identified by the resource description 411 in the applicationrouting table 400. In other embodiments, the client agent 120establishes a plurality of transport layer connections to each of themultiple resources 411 identified by the application routing table 400.In one embodiment, the application routing table 400 identifies to theclient agent 120 an ordered list of resources 411 to use for accessingan application by the client 102. For example, the first resource 411Aassociated with an application is used by the client agent 120 foraccessing the application. If the first resource 411A is not usable,then the client agent 120 may uses the second resource 411B in theordered list, and so on.

At step 715, the client agent 120 via the monitor 500 monitors thestatus of resources identified by the application routing table 400. Inone embodiment, the monitor 500 may check or obtain a status of any ofthe resources, such as appliances 200, on a predetermined frequency,such as every 1 msec or every 1 sec. In other embodiments, the monitor500 may check or obtain a status of any of the resources upon detectingan appliance 200 is unavailable or unusable. In some embodiments, themonitor 500 may use a request/reply mechanism to obtain a status fromthe resource. In other embodiments, the monitor 500 may use any type andform of protocol to obtain a status of the resource. In someembodiments, the monitor 500 uses any of the following to check orobtain the status of a resource: ping or other ICMP command, ftpcommand, http or http command or request. In other embodiments, themonitor 500 sends a request for content to a resource and verifies theresponse is as expected.

In some embodiments, the monitor 500 checks whether a status of aresource is up or down, or otherwise operation or not operational. Inother embodiments, the monitor 500 checks whether a status of a resourceindicates if the resource is performing or operating in a desiredmanner, such as if the resource is under utilized or over-loaded, hastoo many or not enough connections, is servicing too many requests ortoo little requests, etc. In another embodiment, the monitor 500 checks,verifies or validates the response time from a resource is within apredetermined range or otherwise is not beyond any predeterminedresponse time threshold. The monitor 500 may use any representation ofresponse time for a threshold or range of response times, such asaverage, median or any other statistic or historical response timecalculation.

At step 720, the client agent 120 determines via monitoring that thestatus of the resources indicates a resource is not useable by theclient to communicate to the server 106. In some embodiments, themonitor 500 monitors each of the resource on a predetermined frequency.In another embodiment, the monitor 500 monitors the resource currentlybeing used by the client 102 to access the server 106. In oneembodiment, the monitor 500 detects that the status of a resource isup/operational/usable/available or down/not operational/unusable/notavailable. In other embodiments, the monitor 500 detects that the statusindicates the resource is up but not in state that is desirable to beused by the client 102. As such, in some cases, a resource may beconsidered unusable or unavailable when the resource is not performingor operating in a desired manner. For example, the monitor 500 maydetect that the status of the resource indicates a response time isbelow or above a predetermined threshold, and thus, the client 102 mayconsider using another resource to access the server 106.

At step 725, the client agent 120, automatically in response to thedetermination, establishes a second transport layer connection to accessthe server 106. In one embodiment, the client agent 120 establishes thesecond transport layer connection between the client and a resource tobypass the resource identified as unusable or unavailable. In anotherembodiment, the client agent 120 establishes the second transport layerconnection between the client and the server to bypass the resourceidentified as unusable or unavailable. In yet another embodiment, theclient agent 120 automatically switches to a second transport layerconnection previously or already established between the client and theresource or the server. For example, the client agent 120 mayautomatically establish multiple tunnels to multiple appliances inaccordance with the application routing table 400. In one embodiment,the client agent 120 automatically connects to or switches to anotherresource based on the ordered enumerated list identified by theapplication routing table 400.

In view of the structure, functions and operations of the appliance andclient described herein, the client agent provides a high-availabilitysolution for accessing an application or server via multiple gateways,appliances and/or routes, including bypassing a gateway or resource togain access to the server. The client agent 120 can performload-balancing, switching and bypassing automatically and transparentlyto any user or application of the client to provide a seamless andcontinues access experience to an application. The application routingtable and appliance described herein provide system administrators aconfigurable and convenient way to specify failover or continuousavailability paths and appliance gateways that clients should use inaccessing an application or server.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for using a client agent to route client requests among aplurality of appliances using transport layer information, the methodcomprising the steps of: (a) establishing, by a client agent executingon a client, a first transport layer connection with a first applianceof a plurality of appliances, the first appliance providing access toone or more servers; (b) establishing, by the client agent executing onthe client, a second transport layer connection with a second applianceof the plurality of appliances, the second appliance providing access toone or more servers; (c) intercepting, by the client agent, a packettransmitted by the client; (d) selecting, by the client agent, one ofthe first transport layer connection or the second transport layerconnection to transmit the intercepted packet based on a characteristicof at least one of: the first transport layer connection, the secondtransport layer connection, one or more of the plurality of appliances,or the one or more servers; and (e) transmitting the intercepted packetvia the selected connection.
 2. The method of claim 1, wherein at leastone of the first and second appliances is a virtual appliance.
 3. Themethod of claim 1, wherein the first and second appliances are virtualappliances executing on the same physical appliance.
 4. The method ofclaim 1, wherein step (a) further comprises establishing, by the clientagent, an encrypted connection with at least one of the plurality ofappliances.
 5. The method of claim 1, wherein step (b) comprisesestablishing, by a client agent executing on the client, a secondtransport layer connection with the first appliance.
 6. The method ofclaim 1, wherein step (c) comprises intercepting, by the client agent, apacket transmitted by the client, wherein the interception occurs at oneof the following layers of a network stack of the client: thepresentation layer, the session layer, the transport layer, or thenetwork layer.
 7. The method of claim 1, wherein step (d) comprisesselecting by the client agent, one of the first transport layerconnection or the second transport layer connection based on a usage ofone or more servers.
 8. The method of claim 1, wherein step (d)comprises selecting by the client agent, one of the first transportlayer connection or the second transport layer connection based on theusage of one or more of the plurality of appliances.
 9. The method ofclaim 1, wherein step (d) comprises selecting by the client agent, oneof the first transport layer connection or the second transport layerconnection based on available bandwidth of the first and secondtransport layer connections.
 10. The method of claim 1, wherein step (d)comprises selecting by the client agent, one of the first transportlayer connection or the second transport layer connection based on thegeometric distance of one or more servers from the client.
 11. Themethod of claim 1, wherein step (d) comprises selecting by the clientagent, one of the first transport layer connection or the secondtransport layer connection based on the geometric distance one or moreof the plurality appliances from the client.
 12. The method of claim 1,wherein step (d) comprises selecting by the client agent, one of thefirst transport layer connection or the second transport layerconnection based on the availability of one or more servers.
 13. Themethod of claim 1, wherein step (d) comprises selecting by the clientagent, one of the first transport layer connection or the secondtransport layer connection based on the availability of one or moreservers.
 14. The method of claim 1, wherein step (d) comprises selectingby the client agent, one of the first transport layer connection or thesecond transport layer connection based on a security characteristic ofat least one of: the first transport layer connection, the secondtransport layer connection, one or more of the plurality of appliances,or one or more servers.
 15. The method of claim 1, further comprisingthe step of performing, by the client agent on one ore more interceptedpackets, one of the following acceleration techniques: compression; TCPconnection pooling; TCP connection multiplexing; TCP buffering; andcaching.
 16. The method of claim 1, further comprising the step ofreceiving, by the client agent from one or more of the plurality ofappliances, information identifying a characteristic of at least one of:the first transport layer connection, the second transport layerconnection, one or more of the plurality of appliances, or one or moreservers.
 17. The method of claim 1, further comprising the step ofreceiving, by the client agent from one or more of the plurality ofappliances, information identifying the usage of at least one server.18. The method of claim 1, further comprising the step of receiving, bythe client agent from one or more of the plurality of appliances,information identifying the availability of at least one server.
 19. Themethod of claim 1, further comprising the step of receiving, by theclient agent from one or more of the plurality of appliances,information identifying the geometric distance from the client of atleast one server.
 20. The method of claim 1, further comprising the stepof receiving, by the client agent from one or more of the plurality ofappliances, information identifying the availability of at least one ofthe plurality appliances.
 21. The method of claim 1, further comprisingthe step of receiving, by the client agent from one or more of theplurality of appliances, information identifying the usage of at leastone of the plurality appliances.
 22. The method of claim 1, furthercomprising the step of receiving, by the client agent from one or moreof the plurality of appliances, information identifying the geometricdistance from the client of at least one of the plurality appliances.23. The method of claim 1, further comprising the step of receiving, bythe client agent from one or more of the plurality of appliances,information identifying a security characteristic of at least one of:the first transport layer connection, the second transport layerconnection, one or more of the plurality of appliances, or one or moreservers.
 24. A computer-implemented system for using a client agent toroute client requests using transport-layer information, the systemcomprising: a client computing device; and a client agent executing onthe client computing device which establishes a first transport layerconnection with a first appliance of a plurality of appliances, thefirst appliance providing access to one or more servers; establishes asecond transport layer connection with a second appliance of theplurality of appliances, the second appliance providing access to one ormore servers; intercepts a packet transmitted by the client; selects oneof the first transport layer connection or the second transport layerconnection to transmit the intercepted packet based on a characteristicof at least one of: the first transport layer connection, the secondtransport layer connection, the plurality of appliances, or the one ormore servers; and transmits the intercepted packet via the selectedconnection.
 25. The system of claim 24, wherein at least one of thefirst and second appliances is a virtual appliance.
 26. The system ofclaim 24, wherein the first and second appliances are virtual appliancesexecuting on the same physical appliance.
 27. The system of claim 24wherein the client agent establishes an encrypted connection with atleast one of the plurality of appliances.
 28. The method of claim 24,wherein the client agent establishes a second transport layer connectionwith the first appliance.
 29. The system of claim 24 wherein the clientagent intercepts a packet transmitted by the client, wherein theinterception occurs at one of the following layers of a network stack ofthe client: the presentation layer, the session layer, the transportlayer, or the network layer.
 30. The system of claim 24 wherein theclient agent selects one of the first transport layer connection or thesecond transport layer connection based on a usage of one or moreservers.
 31. The system of claim 24 wherein the client agent selects oneof the first transport layer connection or the second transport layerconnection based on the usage one or more of the plurality ofappliances.
 32. The system of claim 24 wherein the client agent selectsone of the first transport layer connection or the second transportlayer connection based on available bandwidth of the first and secondtransport layer connections.
 33. The system of claim 24 wherein theclient agent selects one of the first transport layer connection or thesecond transport layer connection based on the geometric distance of oneor more servers from the client.
 34. The system of claim 24 wherein theclient agent selects one of the first transport layer connection or thesecond transport layer connection based on the geometric distance one ormore of the plurality appliances from the client.
 35. The system ofclaim 24 wherein the client agent selects one of the first transportlayer connection or the second transport layer connection based on theavailability of one or more servers.
 36. The system of claim 24 whereinthe client agent selects one of the first transport layer connection orthe second transport layer connection based on the availability of oneor more servers.
 37. The system of claim 24 wherein the client agentselects one of the first transport layer connection or the secondtransport layer connection based on a security characteristic of atleast one of: the first transport layer connection, the second transportlayer connection, one or more of the plurality of appliances, or one ormore servers.
 38. The system of claim 24 wherein the client agentperforms on one ore more intercepted packets, one of the followingacceleration techniques: compression; TCP connection pooling; TCPconnection multiplexing; TCP buffering; and caching.
 39. The system ofclaim 24 wherein the client agent receives from one or more of theplurality of appliances, information identifying a characteristic of atleast one of: the first transport layer connection, the second transportlayer connection, one or more of the plurality of appliances, or one ormore servers.
 40. The system of claim 24 wherein the client agentreceives from one or more of the plurality of appliances, informationidentifying the usage of at least one server.
 41. The system of claim 24wherein the client agent receives from one or more of the plurality ofappliances, information identifying the availability of at least oneserver.
 42. The system of claim 24 wherein the client agent receivesfrom one or more of the plurality of appliances, information identifyingthe geometric distance from the client of at least one server.
 43. Thesystem of claim 24 wherein the client agent receives from one or more ofthe plurality of appliances, information identifying the availability ofat least one of the plurality appliances.
 44. The system of claim 24wherein the client agent receives from one or more of the plurality ofappliances, information identifying the usage of at least one of theplurality appliances.
 45. The system of claim 24 wherein the clientagent receives from one or more of the plurality of appliances,information identifying the geometric distance from the client of atleast one of the plurality appliances.
 46. The system of claim 24wherein the client agent receives from one or more of the plurality ofappliances, information identifying a security characteristic of atleast one of: the first transport layer connection, the second transportlayer connection, one or more of the plurality of appliances, or one ormore servers.